Field Report: Blackjack Uzi Buffers

[MACVSOG]

A friend of mine has a set of black buffers and a set of green buffers made by Randy. We took them out today to test. I used a PACT timer that is able to measue ROF (rate of fire). First thing is that shooting my .45 conversion kit in my uzi, it definintely was not as harsh when I added one of the 3/8 inch buffers. Now, checking the ROF with 9mm ammo, we found that the ROF was faster with hotter ammo. We used PMC 124 grain FMJ 9mm and Walmart Winchester 115 grain FMJ 9mm ammo. The Walmart is hotter than the PMC. With the PMC ammo, the ROF was 570 RPM without any buffers, and with the Walmart Winchester ammo, the ROF was about the same. So, even though the Walmart ammo was hotter, it did not affect the ROF without any buffers present. But then with the 1/2 inch black buffer and PMC ammo, the ROF was only 573 PM, while with the Walmart ammo, it had a ROF of 673 RPM. Then with all three of his black buffers (1/2 inch, 3/8 inch, and 1/4 inch) using the PMC ammo, we had a ROF of 653 RPM but with the Walmart Winchester ammo, we had a ROF of 849 RPM. We then tried two of he 1/2 inch buffers with two of the 3/8 inch buffers and with the PMC ammo, we had a ROF of 748 RPM, but with the Walmart Winchester ammo, we had a whopping ROF of 990 RPM! The green buffers and the black buffers seem to work about the same. Randy said the green buffers were softer. I have sent this info on to Randy. I believe he is really onto something with these buffers. I am going to do some more experimenting with them, and I will get back to you about what I find. These buffers really allow fine tuning of your ROF for the particular ammo you are using. Since I generally use Walmart, I will not have to use as many buffers to get the ROF that I want. I had been using a semi-auto buffer but found its ROF too fast, but I cannot find the actual figures right now. I will test it again later. What I like about Randy's buffer setup is that you have more than just slow and very fast to choose from as you would either using no buffer or using the semi-auto buffer. With Randy's setup, you can adjust the ROF gradually until you reach the ROF that is ideal for you. With me, I like a ROF of around 750 RPM with a subgun. I have read that 550 RPM is ideal, but I find that with a little faster ROF, I can gett more bullets into the killing zone before the muzzle climb takes me off of target.

Charles Tatum
Alamo Professional Arms

[MACVSOG]

I just e-mailed Randy. He will be doing some more development of different thickness of buffers. I am going to do some testing for him. What we need to know are the various types of 9mm ammo we need to test with each thickness of buffer to give you a ROF for each type of ammo. I have already tested PMC 124 grain and the Walmart Winchester 115 grain. I have some PMC 115 grain and some Federal 147 grain or whatever that Federal ammo is that has the truncated cone FMJ and is subsonic. I have some in my garage but do not want to go run it down right now. I also have a few other brands. So, let us know what brands of ammo you would like to have tested.

Charles Tatum
Alamo Professional Arms

[RoverDave]

Excellent information Charles! Thanks for posting it.

[Gun Shot]

MACVSOG -

Thank you for the test results, this is invaluable information. Please keep us posted on your findings as Randy progresses with tweaking the design. Good job to both you and Randy, thank you.

[montana_jeepn]

I was wondering if there are any long term negative effects on your Uzi from putting in larger buffers? Does this cause any accelerated wear on any of the components? Thanks!

M_J

[MACVSOG]

Actually the buffers remove one form of stress, which is the bolt hitting hard against the back of the receiver. With the increase in the ROF you would increase the wear on the gun if you are tempted to shoot more ammo due to the increase ROF. So, hypothetically speaking, say you generally go to the range and shoot 500 rounds through your Uzi with your 570 RPM ROF. Now because you can change the ROF, and you are enjoying shooting your Uzi more, you might shoot 1000 rounds. So, the buffers would double the wear on your Uzi because you are enjoying yourself and shooting more, not because there is any mechanical reason for it. Remember, Uzi's are made for combat, and as such, they are made to take a lot of use and abuse. I doubt seriously that any of us can replicate what happens in combat by our weekend shooting at the range. It reminds me about the use of the CAR15 during the Vietnam War. The Special Ops guys on MACVSOG did not have a problem with reliability of the CAR15 like some units did. What they found was that the main problem of reliability, besides keeping the weapon clean, was due to magazine problems. So, to check their mags out, some of the MACVSOG guys would shoot a complete combat load (just over 400 rounds) through their CAR15's to make sure all of their mags worked. So, to them, 400 rounds was no big deal and just a way to check mags. To us, who paid big bucks for our M16's, 400 rounds was a day at the range. So, in combat, weapons are subject to much more use, and we do not have to worry that we will replicate this use by shooting on the weekends. The addition of buffers will do nothing to increase the wear on your Uzi. Dragging the Uzi through sand and leaving it in the rain and shooting 5K to 10K rounds through it a month will just push it to its combat limits. Buffers that will increase the ROF do nothing more than take the shock out of the bolt.

Charles Tatum
Alamo Professional Arms

[MACVSOG]

I went out to do some more testing of buffers. This time I only used Walmart Winchester ammo. I first tried one of the CDNN semi-auto buffers (it is 1 1/2 inches thick) and got a ROF of 1015 RPM. I then tried a combo of Blackjack Buffers with two of the black 1/2 inch buffers and one of the black 3/8 inch buffers (a total of 1 3/8 inches thick) and got a ROF of 909 RPM. I then tried two of the black 1/2 inch buffers (a total of 1 inch thick) and got a ROF of 814 RPM. With just one of the 1/2 inch buffers, I got a ROF of 697 RPM. Randy has been working on maybe making a kit of buffers with one 1 1/2 inches thick, one 1 1/4 inches thick, and one that would be 1 inch thick. With Walmart ammo, that would give you about 1000 RPM, 900 RPM, and 800 RPM. I personally like the 700 RPM and sometimes the 800 RPM, so for me I would want some of the 1/2 inch buffers for 700 RPM and some of the 1 inch buffers for 800 RPM. It is better to have a buffer that is the proper thickness rather than use a stack of buffers, as with the stack of buffers, you get some binding, and that causes the ROF to vary while the weapon is firing.

Charles Tatum
Alamo Professional Arms

[Blackjack]

I should have my proto-types early this week, with field testing and documentation I'm guessing 2-3 weeks if all goes well.

[Gun Shot]

Randy has been working on maybe making a kit of buffers with one 1 1/2 inches thick, one 1 1/4 inches thick, and one that would be 1 inch thick. With Walmart ammo, that would give you about 1000 RPM, 900 RPM, and 800 RPM.

That would be SWEET. I also agree that 1/2 inch buffers are still nice, as the slower ROF really appeals to some folks. Personally, I'd be very interested in a kit with the above mentioned thicknesses, that also includes a 1/2 incher for the slower ROF. Gotta have a little bit of that flavor for everyone!

Thanks MACVSOG for the test results, and BJ for keeping us updated on your progress. Exciting stuff!

[subgunner]

Local rental range has 3,000,000 rounds thru an UZI. Yes that's MILLION. They have replaced springs, sears, barrels and one bolt.
Back end of receiver needed a reweld from stress cracks at 2,000,000 rounds. Will you wear out an Uzi? Highly unlikely.

[Vegas SMG]

Subgunner. BEAUTIFUL display of subgun skill at Sunday's match!
First place finish in OPEN class, and the best time of the entire day. Congrats!

I'm sure you noticed I got beaten out of top spot in STOCK class by a girl. My only goal for the season is to beat Jane just once!

[subgunner]

Jane and the AM180 is tough with the right course of fire. Next month's match will require mandatory mag changes that means the 180 stays in the safe so you will have your shot.:angel3

[Blackjack]

I just picked up the first couple 1.5" buffers today, they turned out better than I had expected. I'm getting several more and will cut them down and have them checked for the ROF.
From what I'm reading here it looks like I'll be offering these in .25,.5,1,1.25,and 1.5" lengths with a discount available when buying an asortment of 3 or more.

[Gun Shot]

You da man Randy, thanks for the update.

[texasvwnut]

Woo Hoo!!

[stymie]

Blackjack...

As that is pushing the upper envelope on speed & safety!

[Blackjack]

I'll just have to see how the test results come in, if I need to limit it to 1.4" it's not that big of deal to do so.

[MuzzleFlash]

I don't want to start a flame fest, but I was told by a C2 friend that the 1.4" buffer is way too much for 9mm and is especially a bad idea when shooting .45. His explanation was a bit complicated, but it had to do with the stress on the receiver - especially the rear welds. This stress is proportional to the rate of transfer of kinetic recoil energy from the bolt and the locality of the transfer (point loading).

An ideal scenario matches the ammo, bolt mass and recoil spring and transfers recoil energy either at reinforced hard points or over a large surface area. If you plot the energy transfer rate over the period of time it takes the gun to cycle, it would look like a bell curve with some small spikes - none of which would exceed a safe maximum.

If the bolt "bottoms out" on the back of the receiver, you get a big spike localized to a small area as the residual bolt energy is nearly instantaneously transfered to the receiver. Buffers alleviate this problem.

Can a buffer be too large? Certainly if there are ROF related controlability or feeding problems. Certainly if the sear and safeties don't reliably work. But what about stress on the receiver?

Imagine a large buffer that encounters the bolt at a point where the bolt energy is near its peak. As an extreme example, assume the buffer were made of something hard like steel, it would instantly stop the bolt and send a monster energy spike to the rear of the gun probably breaking the welds and doing all sorts of collateral damage. Clearly, there is more energy to deal with and the demands on large buffers are greater than small ones.

Back to the point. Buffers are obviously made of material that is elastic and tolerant to heat and fatigue. Sort of like a very stiff spring. For a large buffer to be safe, it has to take this maximum bolt energy and store some of it, dissipate some of it (heat) and transfer some of it to the receiver in a manner that won't damage the gun. The buffer may be elastic, but not compared to the recoil spring. Not much energy is lost to heat. Most energy transfers to the receiver and over a considerably shorter interval. The buffer will also expand laterally which, if excessive, may introduce another type of receiver stress not enginered for.

So how much stress is too much for a well made Uzi receiver? No one want's to be the one who collects that data point. For me, I'll keep my buffers short and limit them to operating at lower bolt energies near the travel limit. Especially when shooting .45.

I wonder if nonlinear recoil springs have been tried on Uzis with any luck? I know they are used in some pistols designs.

[MACVSOG]

I would not worry about the damage done to the rear of the receiver as the buffers are thick enough to absorb the energy of the steel bolt. The main thing to consider is that what the buffers do is to limit the travel of the bolt. Rather than traveling all the way to the rear of the receiver and contacting the thin factory buffer, the bolt travel is shortened by the width of the buffer. The the ROF may increase, but it does not increase the amount of energy imparted to the bolt in its rearward motion. If you are using the same ammo, then the same amount of kinetic energy is imparted to the bolt with or without one of blackjack's buffers. If the bolt does not have as far to travel, then you get a faster return to pick up another round, and this increases the ROF. Using very hot +p+ ammo would impart more energy to the rear of the receiver, but a buffer used to increase the ROF does not change he amount of kinetic energy. As far as the buffer thickness goes, I tried a stack of blackjack's buffers that were a total thickness of 1.75 inches. That was too thick as you could not get the racheting handle to come back far enough to engage the bolt and return forward without first taking out the loaded magazine. The buffer that was 1.5 inches worked like a champ. I do not believe we will have any problems with increase ROF on the receiver and I believe that the 1.5 inch buffer will work fine. I think the ROF of the 1.5 inch buffer is a bit much - 1015 RPM using Walmart Winchester ammo. Once we have the new buffers, we will do ROF tests on a variety of ammo. You will find that different brands will have different ROF with each buffer.

Charles Tatum
Alamo Professional Arms

[MuzzleFlash]

Originally posted by MACVSOG
... The the ROF may increase, but it does not increase the amount of energy imparted to the bolt in its rearward motion. ...
Charles Tatum
Alamo Professional Arms Charles

For the record, I want to let everyone know I'm not picking on Blackjack (or CDNN's buffers for that matter). I've heard wonderful things about Blackjack's quality and and his customer service. This is about buffer size and whether or not longer buffers could in theory cause increased receiver stress.

I agree with the above quoted statement. However, destructive stress is caused by the rate of energy being transferred, not the amount (the difference between the energy in a candle and a stick of dynamite is small, but the rate at which they expend energy makes a huge difference in their destructive effect).

For simplicity's sake, lets assume we're using ammo that doesn't overdrive the bolt. This same ammo will be used for all three examples. We'll also assume the reverse and forward bolt motion intervals for a given setup are the same (probably not true in practice)

As an engineer geek, I can't resist a graph even if it's a crude hand drawn one. This graph represents the rate of energy transfer into the receiver body during the rearward bolt movement. The forward bolt would be similar, but at lower amplitude.

http://uziworld.com/miscpics/curves.jpg

Example 1: 600 RPM (100 ms cycle time) with only a standard recoil spring. Half of the bolt's energy is transferred and stored as potential energy in the recoil spring during the bolt's 50 millisecond rearward interval. The spring's resistance (and Newton's third law) provides the transfer of the equal and opposite half of recoil energy into the receiver/shooter mass as kinetic energy. The rate of that transfer is over the rearward bolt stroke is shown by the black curve.

Example 2: Red curve. Doubling the ROF from say 600RPM to 1200RPM by just using a stiffer spring would double the rate of energy transfered to the receiver because the interval was cut in half yet as you pointed out, the energy imparted to the bolt is the same (i.e. the area under the different curves is the same). Because a spring is used over the entire stroke, the curve remains bell shaped.

Example 3: Blue curve. But using a large buffer to get 1200 RPM is not the same thing. First of all, far less energy is being stored in the recoil spring because rearward travel is interrupted by the buffer. It's the buffer that receives the lion's share of the bolt's energy and has to deal with it (by compression and lateral expansion - both of which impart energy to the receiver).

At first the blue curve tracks the black one. No suprise since only the recoil spring is resisting the bolt. However, when the buffer is encountered, it is far less yielding than the recoil spring and it rapidly decelerates the bolt. As you indicated, the bolt had the same amount of energy but most of that energy is being dumped during the last few milliseconds of travel when it engages the buffer. That spikes the RATE of energy transfer back to the receiver. Depending on the buffer characteristics, the blue curve could be very narrow and tall (bad) or it could be wider and shorter (good).

I doubt that it would ever approach the red curve because to do so would require it to be as elastic as a spring.

So that brings me back to my decision to use a small buffer as a means of avoiding bolt contact with the rear of the receiver. The bolt energy is much lower at that point because most of it's energy is stored in the recoil spring or already transferred to the receiver as recoil energy. (Kinetic energy is porportional to the bolt speed squared) The buffer impact spike is much less traumatic than the spike of metal to metal bolt/receiver impact it's preventing.

For ROF tuning, I'd prefer to experiment with springs since they do a better job of spreading out the energy transfer.

Finally - none of this physics stuff really matters much as long as the blue curve in the above chart stays below the level at which receiver stress or fatigue could occur - for all types of ammo that will be used.

My $.02. YMMV.

[Blackjack]

Here's what's going for ROF testing....
.5 .75 1 1.25 1.4 1.5

Surely out of all these 3 can be chosen. What's being tested is the hardest material I use, I can also make these using softer materials if needed.

[subgunner]

Very interesting information on the potential stress of buffers.
But I think your last paragraph said it all:

Finally - none of this physics stuff really matters much as long as the blue curve in the above chart stays below the level at which receiver stress or fatigue could occur - for all types of ammo that will be used.

My anectodal observation of rental range UZI's suggest to me that a buffer, just as IMI uses in the semi, is not likely to cause any damage to a receiver in normal use.

While springs may be a superior solution they are not readily available.


:heavy

[MuzzleFlash]

Originally posted by subgunner
...
My anectodal observation of rental range UZI's suggest to me that a buffer, just as IMI uses in the semi, is not likely to cause any damage to a receiver in normal use.

While springs may be a superior solution they are not readily available.
:heavy Probably OK. IIRC, believe the semi has a striker that is on springs though so when it hits the buffer, wouldn't the springs take up some of the impact (i.e. widen the blue curve)?

The C2 who got me going on this said he had seen cracked welds on a FA receiver but was pretty sure it happened shooting .45 with fairly large buffers. In particular, he chastised me for using a CDNN buffer cut to 1.3".

There's bound to be a big difference in bolt energy between 9mm and .45. However since most .45 kits use the standard 9mm recoil spring, one would expect that a small buffer of some sort would be needed to protect the rear receiver from bolt impact.

I own a Vector and I'm pretty sure it could handle the punishment, but I'd rather not take the small chance it won't. At the very least, if you're going to use large buffers, you may want to err on the soft side and avoid the really stiff ones like CDNN sells.

I hear you on the springs. If anyone knows of a good source for custom made springs (Wolf?), please lemme know.

[MACVSOG]

Randy sent me a complete set of buffers to test for ROF. The set consisted of buffers that were .50", .75", 1.00", 1.25", 1.4", and 1.5" in thickness. We had found that using stacks of buffers caused binding and a change in ROF while you were shooting. So, Randy decided to make some solid buffers to see how they performed. I used Walmart Winchester 115 gr ammo and PMC 124 gr. Here are the results:
1.5" Buffer - 1020 RPM (Winchester) - 836 RPM (PMC)
1.4" Buffer - 978 RPM (Winchester) - 817 RPM (PMC)
1.25" Buffer - 933 RPM (Winchester) - 791 RPM (PMC)
1.00" Buffer - 848 RPM (Winchester) - 708 RPM (PMC)
.75" Buffer - 787 RPM (Winchester) - 590 RPM (PMC)
.50" Buffer - 717 RPM (Winchester) - 579 RPM (PMC)

The ROF with both types of ammo using the original equipment thin buffer is about 565 - 570 RPM.

I also had some American Eagle 147 grain subsonic in truncated cone and gave that a try with the 1.4, 1.00, and the .75 inch buffers. That ammo apparently is pretty hot even though it is subsonic (heavier bullet keeps it subsonic). ROF for the American Eagle ammo was 999 RPM with the 1.4 inch buffer, 866 RPM with the 1.00 inch buffer, and 792 RPM with the .75 inch buffer.

Randy is going to decide what length buffers to offer in a kit. I suggested that he have a kit with the .5, 1.00, and then either the 1.4 or 1.5 inch buffers. I also found that Randy's 1.4 and 1.5 inch buffers are much easier to install and remove than the CDNN semi-auto buffer that had been cut down. The semi-auto buffer is a little too thick and binds once it is in the receiver. I had to use a punch through the hole in the back of the receiver where the wooden stock attaches to knock out the buffer. I don't know what I would have done if I had a folding stock on it. Maybe others have filed down the sides of their semi-auto buffers to facilitate taking them out. At any rate, Randy's thickest buffers are just the right size, so they are very easy to take out. I really like being able to change the ROF of my Uzi. A faster ROF allows me to put three round bursts with a tighter group. I did the same thing with my Greasegun, but with it I changed the springs using different length Thompson SMG springs to speed up the ROF. I don't want a buzz gun, but I do like my ROF around 700 to 750 RPM. As you can see by the testing, to achieve a specific ROF, you have to consider what type of ammo you are shooting. So, if I am using Walmart Ammo, then I would want to put in a .5 or .75 inch buffer to get the ROF just over 700 RPM. However, if I am shooting the PMC, then I would need to put in either a 1.00 or 1.25 inch buffer to achieve that same ROF. I think that the buffers will give us more flexibility with our shooting. We can already change the caliber of the Uzi if we want to. Now we an change the ROF also.

Charles Tatum
Alamo Professional Arms

[Blackjack]

I'm trying to have them ready for the Knob Creek shoot in Oct. if I do it's going to be close. November should be no problem.

[Blackjack]

I've got (5) 1.5" buffers for sale if anyone's interested, the 3-pack kits should be available sometime next week.

1.5" will be $12.95 + s/h

[Blackjack]

OK Guys,
I have 8 of the 3-pack sets ready and 5 of the 1.5" buffers. Any Uzi buffers that aren't sold tonight are going to the Creek with me tomorrow.

3-packs (.75",1",1.25") are $26 + s/h
1.5" are $12.95 + s/h

[Gun Shot]

I wish I would have had a chance to check the site last night...I totally missed this.

Blackjack, let us know when the new 3-pack batch (hard) gets made up after you return from The Creek. My Vector will be here probably by Christmas, so it's time to order some buffers to prepare! :uzi

[Blackjack]

I'm back and have a few 3-pack kits left with more to come.

[texasvwnut]

Blackjack -

I want one of the 3-pack kits. I'll get payment in the mail this weekend.

[Blackjack]

Oky-doky

[Blackjack]

Here's some pics:

http://blackjackbuffers.com/UZIsm.jpg
.25" (replaces oem buffer)

http://blackjackbuffers.com/Uzi3pk.jpg
.75"-1"-1.25" buffer kit

http://blackjackbuffers.com/Uzi15.jpg
1.5" buffer

I can take the 1.5" down to 1.4" if needed.

All my uzi buffers have the cavity for the stock bolt clearance now.

[Gun Shot]

They're beauties BJ, as soon as the late paycheck comes in I'm ordering my 3-pack. I might also have to get you to cut one of the 1.5's to 1.4 for me :D :uzi .

[stymie]

Blackjack...

...or is there a surcharge for cutting them down? I'd like to get a 3 pack & a 1.4".

Thanks!

[Gun Shot]

I'm w/ Stymie on that one.

[Blackjack]

No sur charge, untill I get a 1.4" mold made I just take them down manually.

[Blackjack]

I just want to let all of you that have ordered the 3-pack and 1.4" buffers in the last week or so but haven't received them yet know that my urethane source hasn't been pouring any of the black that I use for the last couple weeks. I have been told that he will resume on Monday so hopefully I'll be able to fill your orders by the end of next week.

Sorry for the delay.

[Blackjack]

The 3-packs and 1.4" buffers are in stock now and any back-orders will be filled tonight.

Thanks for your patience.