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Semi-Auto Hard To Cock? Its Not Your Imagination...


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The difficulty of cocking the semi-autos is a topic here now and then.

I have read that 27-29 lbs is considered to be the norm and actually measured

that here in the shop.

Lately though, I have worked on several guns that I could not cock in the

normal fashion - by pulling back the bolt, but would have to hold the cocking

handle against a workbench and push the rifle to cock the gun. This has

happened again so I figured I would measure the force required, because I

can handle 29 lbs, but not these recent rifles.

The bolt is relatively easy to cock for the beginning of rearward travel.

Then you hit a hard spot where the firing pin is caught by the sear and an

even harder spot where the bolt catch is activated.

The rifle I checked which is factory-new requires between 40-42.5 lbs, of

force to retract the bolt back far enough to cock the bolt to the full recoil

position which would cock the firing pin and activate the bolt hold open.

However, with the magazine in the gun the trip acting on the bolt catch

creates more friction and a force of between 50-55 lbs is needed to retract

the bolt far enough to activate the bolt catch.

With this amount of force required to operate the gun there are two problems

I can think of - 1) this amount of force required to cock the gun makes operating

the gun beyond the strength of many. I include myself here. If I was out shooting

I would not be able to cock the gun. 2) This cocking force invites unsafe handling

conditions as the user contorts himself and looks for mechanical aids to be able

to cock the gun.

I do not know why the cocking force has gone from the difficult-but-I-can-do-it

27-29 lbs. to the impossible-can't-do-it 50-55 lbs. But it is something to consider.

Perhaps this is a random thing? For anyone buying one of these I would ask the

sales person to cock the gun for you.

 

Bob

 

Gun with 42.5 lbs drawing bolt to full cock:

 

http://i51.photobucket.com/albums/f392/reconbob/IMG_2802.jpg

 

This is the stack of weights needed to draw the bolt to full cock with an empty

magazine in the gun activating the bolt catch:

 

http://i51.photobucket.com/albums/f392/reconbob/IMG_2803.jpg

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Just go ahead and replace the spring set with one of the "easy cock" variety and be done with it. I got my replacements from Paul K last year and have never once been sorry I did so. With the replacement set installed mine cocks as easy as a 28.

Jim

Edited by james m
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The engineering handbook says it does affect the cycle for blow back operational types. But then again, so would a 40-42 lb spring when a 27-29 lb is called for.

 

Hearing about 40 lbs springs is interesting for anyone who is interested in more than just shooting the

Thompsons'. Let's hear more.

Edited by T Hound
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My semi cycled ok with the original 20 + lb spring in it. I did the replacement to make it easier to cock. For example: My wife couldn't cock it at all making the gun useless to her. I've not measured the current lbs of pressure but it seems to be no more difficult to cock with the conversion then the 28s I have handled and it cycles just fine. I should have indicated this in my previous post but the cost to make the conversion was around $40. IMO: It's not only an easy fix but an inexpensive one as well.

As an aside Bob: At least you got good looking wood on your example!

Jim

Edited by james m
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  • 10 years later...

To ReconBob.  Your post (although 11 years ago) thrilled me.  Short story: I'm near 70 and a retired firefighter.  A retired firefighter friend of mine recently came into possession of an Auto Ordnance WWII (America Remembers) Tribute Thompson #283 of #300, along with several other nice firearms.  He isn't into the firearm hobby and asked if I would take a look at what he had and offer an opinion on collectability and value.  I'm no aficionado either but I agreed.  I had never had contact with any Thompson, original or remake.  He and another gentleman had not been able to draw the bolt back and I also tried.  They did not have the Owner's Manual or any related paperwork.  I had never experienced the kind of resistance attempting to charge a firearm and I have several AR platforms (7.62 and 5.56) plus an M1A.  They were convinced it was a mechanical problem.  Not to be defeated, I started digging and found my way here.  Read your post and looked at the pictures and printed off everything.  Downloaded and printed off selected pages of Thompson Owner's Manuals.  I contacted the guys and went back out this past Sunday with a pair of gloves and a few heavy duty 12" nylon zip ties.  Yep. I wrapped three zips around the bolt while one man held the thing steady.  I pulled hard (no idea of pounds) while he held and when the bolt was in position, the third pulled the bolt up,287172000_20230226_AmericaRemembersWWIITribute.thumb.jpg.627b2b5dcd7bb74957ce93056ec38dd1.jpg to catch.  When I showed up earlier, they both thought I was nuts with the zip ties and papers but I had them read your post and they (hesitatingly) thought "If you want to try it".  I signed up for this board specifically to say "Thank You" and the other members.  I'm going to try and attach a pic of me holding the thing.  Sure wish I could hang it on my wall......

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I bought a new semi M1 SBR from KAHR in 2010 and could barely cock it,  damn! Did feel unsafe because of the pull it took to cock. Weapon shot just fine. Got easy spring kit from Dear slayer here on the board and Wow! What a difference it made.  It felt like a normal Weapon after that. Functions just fine and doesn't seem to be harder on the weapon. It was an easy fix. And inexpensive! 

Though would add my experience on this.

Take care everyone 

 

Edited by Stampcollector
Correct word
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4 hours ago, Stampcollector said:

I bought a new semi M1 SBR from KAHR in 2010 and could cook it but,  damn! Did feel unsafe because of the pull it took to cock. Weapon shot just fine. Got easy spring kit from Dear slayer here on the board and Wow! What a difference it made.  It felt like a normal Weapon after that. Functions just fine and doesn't seem to be harder on the weapon. It was an easy fix. And inexpensive! 

Though would add my experience on this.

Take care everyone 

 

You had better luck than I did! 
 

In 2012 a friend and I did some trading and I ended up with a 1927-A-1 that he bought in 2010. He never fired it and I didn’t either until 2014. Under fifty rounds the bolt locked up, fractured extractor groove, metal embrittlement. Kahr was basically no help, second owner, one year warranty and after a FB complaint a “offer” that was really nothing. Bought a new bolt, extractor and both retaining pins, one for the firing pin and one for the extractor. And, they managed to screw that order up, sent two of the same pins despite the invoice showing different part numbers. Gave up and used one of the old ones over, it would have cost me more to send it back for replacement then the pin so I just tossed it.

The Howell kit is the one I installed, two bolt springs, new hammer and hammer spring and a buffer. Bolt pull is soooo much wiser to pull and no problems with its function either.

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