Rate of fire?

[Kilroy]

I thought the cyclic rate of a Thompson was around 750 rpm (I'm talking '28s here). Doing rough math in a video of me doing a drum dump it burns through 50 rds in about 3.4 seconds. My math makes that 875 rpm, right? Or am I doing math wrong?

[Bob]

They are all over the place. I've timed M1's, M1A1's, 28's and 21's and the only thing I can say for certain is too many variables to say "this ____ Thompson type will run 750 rounds per min. I have a M1 with sand cut bolt that runs 1024 consistently on my reloads (230gn behind 5gn bullseye). That's MAC 10 speed!

 

Think 875 would be about average.

 

[buzz]

(50-1) rounds / 3.4 seconds = 14.41 rounds per second

 

14.41 x 60 seconds = 865 rounds per minute

Edited October 22, 2014 by buzz

[Kilroy]

http://youtu.be/meQq5MMM9Dw

 

Doesn't get old

[mnshooter]

http://youtu.be/meQq5MMM9Dw

 

Doesn't get old

Very Nice.

What kind of ammo were you shooting?

[Kilroy]

Cheap Remington UMC stuff I buy in bulk packs.

[buzz]

You'll probably see the ROF increase a lot if you use ammo other than Remington/UMC

 

It is usually quite underpowered.

 

I fired a MAC M11/9 with it, it ran about 900. Switched to Winchester super x and the ROF went up to at least 1200

[shadycon]

I wonder what it would be using my relaods? Loaded a little hot. Lyman book normal load rated 850 fps, I load to 900 fps rating. Still within lymans safe load data. These will slightly mushroom when hitting an old propane tank. GK

[buzz]

They make a shot timer application for cell phones.

 

It wont measure between shots for full auto but it will measure the duration of the full string

 

that can be used to calculate the ROF

 

or you can videotape the mag dump and use a stopwatch to record the time.

 

 

Divide the total elapsed time in seconds by the number of shots minus one

 

that gives you the time between each shot in seconds

 

Then divide 60 seconds by the time between each shot and you get the ROF in shots per minute

 

 

Example:

 

You time a 30 round mag dump at 2.2 seconds

 

2.2 seconds / (30 -1) = 0.07586 seconds per round

 

60 seconds / 0.07586 = 791 rounds per minute

[mnshooter]

I wonder what it would be using my relaods? Loaded a little hot. Lyman book normal load rated 850 fps, I load to 900 fps rating. Still within lymans safe load data. These will slightly mushroom when hitting an old propane tank. GK

There's really no reason to load hot for a Thompson, and good reasons not to.

The reason not to being: why put unnecessary stress on the gun?

I have seen a Colt Agent revolver taken apart by maximum .38 special loads right out of the book.

 

I have tested 230RN loads down to 30 percent less energy than factory loads, and still got 100% function in a 21, 28s, and M1s. Even loading a 180grain bullet over a powder charge that would be 10% low with 230gr. bullets still gave 100%, and this was with a new Wolff recoil spring (although I have reconsidered the use of the Wolff spring, given Reconbobs recent post on the subject. I also use an extra thick neoprene buffer pad.

[Scott Smith]

My 1928A1 was timed at 850 rpm recently. I was thinking that it was supposed to be down around 650...

 

What options exist to slow down the rate of fire to something closer to 650. Stiffer return spring or ???

 

Scott

[mnshooter]

My 1928A1 was timed at 850 rpm recently. I was thinking that it was supposed to be down around 650...

 

What options exist to slow down the rate of fire to something closer to 650. Stiffer return spring or ???

 

Scott

See Reconbobs recent post regarding heavier recoil springs.

In my experience,

a heavier spring will often increase the rate of fire.

A softer spring that allows maximum bolt travel can decrease the ROF.

The balance you want is longest recoil, without battering the rear of the receiver.

Others have tried adding lead to the bolt/actuator combo to increase bolt weight.

The MG42 can use a light or heavy bolt. The light bolt is noticeably faster.

[Guest66]

http://scholarlycommons.law.northwestern.edu/cgi/viewcontent.cgi?article=2366&context=jclc

 

Info on rate of fire from 1933......

[shadycon]

Guest66: Welcome! Very interesting artical! GK

[buzz]

Have you ever seen any thompsons running at 650?

 

Look at videos on the internet, you never see them running that slow.

 

 

Anyway, did you ever shoot an MG at 650? I find that it feels very choppy.

 

Maybe it wouldn't feel that way with a big heavy gun like a Thompson, but it does on lighter guns.

 

A lot of UZI guys put a thick buffer in the gun to speed it up and make it run smoother.

 

 

Personally I think that 800 to 900 RPM is just about perfect for firing an SMG in short bursts

 

 

Anyway, to answer your question,

 

A lot of guys who own MACs want to slow them down, so they use a weaker spring, softer recoiling ammo, or some sort of friction device in the gun.

 

The occasional guy will figure out a way to add weights to the bolt.

 

Or they chop a hole in the back of the gun and add a rod to the bolt that extends thru the gun and into an AR15 stock, and pushes the big buffer weight and spring in the stock. That's actually pretty clever.

 

Seems to me it would be better for them to just learn how to hold and shoot the gun properly.

 

You hear those guys say stuff like "The sights are useless". It's got a large rear peep aperture and a post front sight. How is that useless?

 

 

Also, it's been found a lot of times that when a SMG runs badly and jams, the problem can be solved by using a fresh recoil spring, the limp old springs don't store up enough potential energy to run the gun properly.

 

So chopping coils off a spring is not always going to leave you with a good running gun.

 

Also, the weak spring would tend to make the bolt hit the buffer harder. That's not a worry for a $4000 sheet metal gun but maybe not a good thing for a $25000 thompson

 

 

 

My 1928A1 was timed at 850 rpm recently. I was thinking that it was supposed to be down around 650...

 

What options exist to slow down the rate of fire to something closer to 650. Stiffer return spring or ???

 

Scott

Edited October 25, 2014 by buzz

[dalbert]

Kilroy,

 

Jim C 351 posted an excellent topic a few years ago on rate of fire for the Thompson and Reising. Here is the link:

 

http://www.machinegunboards.com/forums/index.php?showtopic=10534

 

David Albert

dalbert@sturmgewehr.com

[dalbert]

Personally, I don't believe anything stated in military rate of fire specifications listed in manuals of the 1920's to 1940's time period. Case in point, the Reising was listed as running at 450 rpm in period manuals. Try doubling that number for the real rate of fire.

 

The 1928 Navy model had a reduced cyclic rate to the Model of 1921. However, I just don't see it matching what was advertised.

 

David Albert

dalbert@sturmgewehr.com

[Scott Smith]

 

Have you ever seen any thompsons running at 650?

 

Look at videos on the internet, you never see them running that slow.

 

 

Anyway, did you ever shoot an MG at 650? I find that it feels very choppy.

 

Maybe it wouldn't feel that way with a big heavy gun like a Thompson, but it does on lighter guns.

 

A lot of UZI guys put a thick buffer in the gun to speed it up and make it run smoother.

 

 

Personally I think that 800 to 900 RPM is just about perfect for firing an SMG in short bursts

 

 

Anyway, to answer your question,

 

A lot of guys who own MACs want to slow them down, so they use a weaker spring, softer recoiling ammo, or some sort of friction device in the gun.

 

The occasional guy will figure out a way to add weights to the bolt.

 

Or they chop a hole in the back of the gun and add a rod to the bolt that extends thru the gun and into an AR15 stock, and pushes the big buffer weight and spring in the stock. That's actually pretty clever.

 

Seems to me it would be better for them to just learn how to hold and shoot the gun properly.

 

You hear those guys say stuff like "The sights are useless". It's got a large rear peep aperture and a post front sight. How is that useless?

 

 

Also, it's been found a lot of times that when a SMG runs badly and jams, the problem can be solved by using a fresh recoil spring, the limp old springs don't store up enough potential energy to run the gun properly.

 

So chopping coils off a spring is not always going to leave you with a good running gun.

 

Also, the weak spring would tend to make the bolt hit the buffer harder. That's not a worry for a $4000 sheet metal gun but maybe not a good thing for a $25000 thompson

 

 

 

My 1928A1 was timed at 850 rpm recently. I was thinking that it was supposed to be down around 650...

 

What options exist to slow down the rate of fire to something closer to 650. Stiffer return spring or ???

 

Scott

Hi Buzz, thanks much for the info. I don't know that I've ever seen a Thompson running at 650 or not. Back in the 90's when I was competing in Indiana and Wisconsin some of the Thompson guys seemed to have guns that ran slower than others.

 

I have shot MP38's and 40's, as well as Swedish K's that ran around 600 - 650, and in particular I remember one MP38 that was running around 550. He was tough to beat because he never wasted ammo on the range. I recall that the Swedish K's would actually move up and down a bit while the bolt was cycling due to the slow rate of fire.

 

My MP5SD shoots around 700 - 750 rpm, and I like the variety of having some guns that shoot a bit slower.

 

I don't want to make any permanent mods to the gun (or anything that would damage it); based upon your explanations if I did anything it sounds like the first step would be to pick up a spare bolt and perhaps add some weight to it via tungsten inserts in the side of the bolt. Or, I can just leave well enough alone....

[Scott Smith]

Kilroy,

 

Jim C 351 posted an excellent topic a few years ago on rate of fire for the Thompson and Reising. Here is the link:

 

http://www.machinegunboards.com/forums/index.php?showtopic=10534

 

David Albert

dalbert@sturmgewehr.com

That was a great read! Thanks for sharing.