M27A1 with drum - bolt latches open

[krcochran]

I've only had this to the range about 4 times. The first time I had feed problems with both drum and stick magazines. After some maintenance on the magizines they fed better by the third time to the range. The last time the stick magazine worked fine. When I attached the drum magazine and fired the first shot the bolt latched open. I pulled back and released it and it chambered the bullet. The next time I fired it locked back again. I repeated the process about 14 times and gave up after my hand started hurting. Does anyone have any idea why the bolt would lock open. It's not even supposed to do that on the last shot.

Thanks in advance.

[Bawanna]

I'll have to ponder some. My drum acted up the first time but I don't think I had it loaded properly. Since then it hasn't has any issues. I don't shoot it often and haven't for quite awhile, need to remedy that.

The sticks can take some tweaking to get them working properly. Making sure they are fully seated.

I don't have a good answer for you but I'll ponder some, take a peak at mine, try to come up with a workable theory.

[krcochran]

I took it back tot the range today. The bolt still locked open. I put in the stick magazine and to my surprise it locked open then also. I forgot to mention that I am using reloads. The load I used today was 6.2 grains of CFE Pistol with a Speer 230 grain TMJ bullet. The Hogdon manual shows this would produce a velocity of about 850 fps. The Winchester ammo that I have used fairly successfully produced 835 fps. Of course the velocities are based on pistol use. I'm thinking that the load may be the problem but I am also concerned that there may be something else wrong also. IF the problem is the reloads that doesn't explain how the bolt is latching open. More for you to ponder, Bawanna. Thanks

[Bawanna]

First thing I do in a case like yours is try the Winchester ammo that worked before and see if it still balks.

It could easily be too much load or not enough load. Either of which might effect the bolt latching open.

I know they don't care for light loads much but doesn't sound like your are too light to me.

Still pondering.

[krcochran]

The factory ammo was my next plan. I also have some reloads that I got with the rifle that might work. I wasn't ready today to deal with all that. It may take a while to get back to the range now. Or I might go back tomorrow. :)

[Bawanna]

I hate it when I want to test something but can't get to the range for a multitude of reasons.
I have two guns I haven't even shot yet I'm aching to try. Got a set of sights coming for another, so guess I might as well wait another week and take them all to test................

[krcochran]

Well, I took it to the range again today, loaded it with 5 Winchester bullets and the first four worked fine. With the fifth the bolt locked open. Then I loaded 5 bullets loaded withe 6.5 grains of CFE Pistol and they worked ok. I read somewhere that the the Thompson likes hotter loads and the 6.5 load is definitely hotter than what I used originally. I also loaded 5 with 5.9 grans of CFE and those worked ok. I loaded 5 Winchester bullets in the drum. The first time the bolt locked open. The next three worked ok. The last one went diagonal on me. I'm looking at today as being fairly successful, but I still don't understand why the bolt locked open in the first place. Do you know of any documentation that explains the operation of the Thompson and the parts involved.

[Bawanna]

I've also heard the Thompson much prefers hotter loads. The bolt on that puppy weighs a ton, I'm surprised a 45 load will even make it function but it does.
I don't know of any documentation but it must be out there.

I've been chasing my tail for awhile now, haven't really had time to even properly ponder and haven't made it to the range yet either............................

[krcochran]

Thanks, I appreciate your assistance.

[Bawanna]

Smartest guy I know on Thompsons is GhostSoldier but he hasn't been around for quite a spell, don't know if he checks in now and then or not.

I'll try to ring him up.

Earth to GhostSoldier come in GhostSoldier, ya got your ears on gby.

Well by golly he checked in yesterday so he just might see this and come along and give us some help here.

[gb6491]

My experience with Thompson guns is limited to shooting them; I know diddly-squat about their internals.
However, I did find a thread where a fella mentioned that he had issues similar to what krcoachran described. One of the replies in that thread was from was from a member that had the issue in two guns and in both instances the culprit was a weak pawl spring: http://www.machinegunboards.com/forums/index.php?showtopic=4226
Regards,
Greg

[krcochran]

Thanks for the info. At least now I know in what area to look for the problem. Unfortunately it will take a while before I can get back ot the range this time.

[krcochran]

I took it apart an cleaned it today. It was probably under lubricated. There was some friction with the trip lever movement but it didn't stick. Next time to the range I'll find out if it's over lubricated now. ;)

[krcochran]

I took it apart an cleaned it today. It was probably under lubricated. There was some friction with the trip lever movement but it didn't stick. Next time to the range I'll find out if it's over lubricated now. ;)

I finally got it back to the range last Monday. Before I did I replaced the recoil springs with McMaster-Carr springs mentioned in a post elsewhere in these forums. I loaded both the drum and the stick magazine with a mixture of my reloads and factory ammo. Needless to say I was a little apprehensive about the new springs but to my surprise I didn't experience a lock open or a missfeed untill the last round from the drum. That one
tried to go into the chamber backwards. All of my shots, from about 20 yards, were inside the target ring. Most of them were close to the center. I have to say that I am now pleased with my Thompson. I will keep an eye on how well the springs hold up.

Thanks to Bawanna and Ghostsoldier for their help.