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Recoil Forces - A Comparison Experiment


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#1 deerslayer

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Posted 08 September 2020 - 06:40 PM

So I decided a good way to calculate the recoil forces on the back of the receiver would be to squish a piece of lead. This is not going to yield a true measurement in something like foot pounds, but my goal was comparison and I did the first experiment today.

I was gonna use a lead bb held in place by a dab of grease but then decided to use a 22 LR bullet super glued to the buffer. I decided on that because bullets would be uniform starting size and lead composition. And this whole experiment could be easily duplicated by another person wanting to add to the results.

I use the term buffer loosely as an M1A1 buffer with it's solid rivets doesn't provide any buffer cushion what so ever. I inserted one round directly in the chamber with no magazine in place. The goal was to get the straight recoil force of one round. It worked beautifully, the lead had a nice squish. I measured it and will retain it for the comparison to the other guns. I plan to test a 1921 bolt assembly and a 1928 bolt assembly and a semi auto 1927. In the 21 and 28 I will defeat the existing buffer cushion and have straight metal contact for the squish.

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#2 skoda

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Posted 08 September 2020 - 08:29 PM

Clever idea.

 

It would be interesting to see the results of say three shots of the same ammo in the same gun to see if there is consistency or a lot of variation.


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#3 jim c 351

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Posted 08 September 2020 - 08:37 PM

Dan,

You Americans are very clever.

Jim C


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#4 mnshooter

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Posted 08 September 2020 - 09:26 PM

That is a lot of bullet squish. 

Wouldn't have guessed it would have that much impact.

Will be very interesting to see what the other tests reveal.

Looks like Dan's caliper has had a few squishes, too.


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#5 john

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Posted 08 September 2020 - 10:16 PM

Would a trigger scale or a scale of that type possibly work?
I figure you would have something along those lines?
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#6 deerslayer

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Posted 08 September 2020 - 10:53 PM

Trigger scale? The question has been raised over the years how hard does the bolt hit the back of the receiver (in the various Thompson models)...trying to find that out.

When I'm done I was thinking I could start dropping a 1 pound weight on a lead bullet from various heights to get a footpound estimation.
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#7 deerslayer

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Posted 09 September 2020 - 09:13 AM

28 actuator and 21 actuator before and after squishes. Taking out the buffer on the 28th works good the bullet basically became the buffer. I use the same recoil spring as the M1A1 test. On the 21 I use the same bolt and blish lock but 21 actuator, spring and buffler assembly. The bullet was thick enough that the inner urethane buffer did not come into play. The recall all stayed on the larger diameter tube in the assembly against the receiver.

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#8 deerslayer

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Posted 09 September 2020 - 09:17 AM

But now for the shocking (or not so shocking) results.

The M1A1 and the 28th both have the same squish. The 21 has less. Moral of a story throw away your 28th actuators and get a 21. They knew what they were doing when they originally built the Thompson and didn't let any whiny Navy guys get in their way lol...

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#9 deerslayer

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Posted 09 September 2020 - 09:39 AM

And here's the semi-auto results. Factory kahr springs, and easy pull springs by Howell. (I decided to use the Howell springs because I had a new set here not the Merle version springs I also sell). Howell I think essentially copied Merles as they seem to be the same to me). it should come as no surprise that there's a lot more squished into semi-auto especially with the EZ pull springs.

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#10 Bridgeport28A1

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Posted 09 September 2020 - 03:07 PM

But now for the shocking (or not so shocking) results.

The M1A1 and the 28th both have the same squish. The 21 has less. Moral of a story throw away your 28th actuators and get a 21. They knew what they were doing when they originally built the Thompson and didn't let any whiny Navy guys get in their way lol...

 

Dan, inside every 1928 actuator is a 1921 actuator trying to get out.


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#11 anjong-ni

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Posted 09 September 2020 - 07:44 PM

Great experiment.

 

Assuming the 1928's had operating Blish locks.

 

Would be be interesting to see how a '28 did with a "de-ear'ed" Blish, to prove or dis-prove "Metal adhesion" once and for all...Phil


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#12 deerslayer

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Posted 09 September 2020 - 07:54 PM

I thought about doing that.. de eared versions run faster for sure... With the slightly lighter weight compared to an M1A1 bolt it may hit a little harder... But nobody is gonna run one of those so I don't think it matters. My first philidephia ordnance gun was built without the blish locks and I used a nut and bolt to lock the actuator to the bolt. I don't have it anymore or I would have tried it.

Edited by deerslayer, 09 September 2020 - 07:57 PM.

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#13 mnshooter

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Posted 09 September 2020 - 10:42 PM

It still seems like a good idea to also run tests without the blish ears; to show if there is any difference in compression force.

 

Also hoping Dan will repeat the test on the 21 assembly with the pilot tube empty -no buffers inside. 

This would make it a more apples to apples comparison with the 28, which was tested with no buffer.

 

 

In any case, great work, Dan.   As busy as you always are, thanks for taking time to do this.


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#14 deerslayer

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Posted 10 September 2020 - 07:34 AM

In the 1921, the inner "inside buffer" was not compressed or impacted by recoil in this case, the 22 bullet created a bigger gap between the receiver and the outer guide tube than recoil would allow the inner guide to come into receiver contact, even at it's full squish. If you wanna cut the ears off a blish... And send it to me.. I'll shoot it.
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#15 reconbob

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Posted 10 September 2020 - 09:40 AM

Very, very interesting. I am especially fond of the new
concept of "squish". Great job Dan!

Bob
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#16 deerslayer

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Posted 10 September 2020 - 10:28 AM

Well..a nine pound sledgehammer lifted up 6 inches squished the bullet down to 0.1295 inches... So we're talking 4.5 footpounds of energy to more than replicate the recoil force.

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#17 deerslayer

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Posted 10 September 2020 - 10:46 AM

Physics time...

Edited by deerslayer, 10 September 2020 - 10:47 AM.

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#18 deerslayer

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Posted 21 September 2020 - 08:23 PM

Just to add it here... Here is the result of the de eared blish lock.

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