tbirdsc Posted June 21, 2019 Report Share Posted June 21, 2019 Hello All,I am a new member just joining yesterday and this is my first post.I am mostly a WWII 1911A1 guy so this is my first venture out of that realm so I am pretty green when it comes to the Thompson. I am in the process of obtaining a 1988 WH 1927A1 upon which I plan on going the SBR route. I always thought if I was going to go thru all the SBR paperwork, a S/A Thompson would be it so I decided to go for it. After the 1911, the Thompson is my second favorite WWII firearm.With that being said, I have few questions after poring through this forum posts and the web in general. It is my understanding that the closer the WH unit is to the original date of introduction (1975), the greater the chance of it having some USGI parts, furniture and such and the fire control may or may not be modified USGI part- but in a nut shell since my unit is dated to 1988 – use Kahr parts for the fire control group and USGI may be used for the rest if desired or needed? I plan on going with the finned 10.5 barrel and again after poking around on this forum and the web, I am confused on the horizontal foregrip fit. I was assuming they are all the same except for the mounting bar width. However, Numrich lists three foregrips each with a different p/n for a 3/4 inch wide bar alone so I am not so sure now. Are there different forends? – As for the forend width, I have seen USGI surplus units on Gunbroker in both 1/2 or 3/4 inch width? Is the width a manufacturer option or was it a date driven revision. I have noticed that sometimes the Cutts is not pinned – a manufacturing cost issue I assume. What was the logic for not having the mag catch in the USGI position on the WH and Kahr units other than have to use their mags if you did now want to modify USGI mags?Thanks in advance for all the help and I already found tons of info so thanks to all who has posted before.Jim Link to comment Share on other sites More sharing options...
95mustang Posted June 21, 2019 Report Share Posted June 21, 2019 The mag catch is in the usgi position , what's different is the upper receiver is .100 thousands shorter in height so unless you elongate the hole in mag ,the magazine is .100 too tall Link to comment Share on other sites More sharing options...
95mustang Posted June 21, 2019 Report Share Posted June 21, 2019 Or modify the catch to accept usgi mags Link to comment Share on other sites More sharing options...
06AngusSG Posted June 21, 2019 Report Share Posted June 21, 2019 If you are going with a GI spec 10" barrel the best thing to do is just shell out for a 1/2" grip hanger and get a military Thompson foregrip. Then you k ow for a fact all the parts will fit. Philidelphia Ordnance makes a great repro grip hanger. He is user reconbob here on the boards. Good luck and welcome. Jon Link to comment Share on other sites More sharing options...
DeaconKC Posted June 21, 2019 Report Share Posted June 21, 2019 I would recommend modifying the mag catch. Mine uses the modified mags and I was able to swap some originals for modified mags so I came out ahead. As I have about a dozen now, I will continue to use the modified ones. But if I were looking at one like yours and was just starting, the mag release mod would make more sense financially. Link to comment Share on other sites More sharing options...
Vettom Posted June 21, 2019 Report Share Posted June 21, 2019 I am planning to mod my mag catch as I am accumulating non-modified mags... Link to comment Share on other sites More sharing options...
Oldtrooper Posted June 21, 2019 Report Share Posted June 21, 2019 If your compensator doesn't have a hole for a pin it might be a threaded on comp ... Kahr uses a roll pin ... Dan Block put in a regular pin when he put on my 10.5 inch barrel ... BTW ,,, When you change barrels, polish the feed ramp ... My experience is that neither model (West Hurley/Kahr) is what I would call finely finished. Link to comment Share on other sites More sharing options...
mnshooter Posted June 21, 2019 Report Share Posted June 21, 2019 No new news here, but, since you asked for information:The only fully interchangeable GI 28 parts you would find on the majority of semis are the sling swivels, assorted mounting screws, and a spring or two.The GI safety and adjustable Lyman rear sight is also interchangeable, but seldom seen.All "Real" Comps and Barrel assemblies are threaded, in addition to the pin. Some of the semi barrels have a press on comp and possibly a pin.Many (most) of the West Hurley select fire comps use threads, but no pin; Thread locker was used instead.The reason for all the mag catch/receiver height, etc., was a direct result of the Semi Auto ATF approval requirements.All "Real" Thompsons use the 1/2" grip mount bar. Most of the semi 3/4" bars are aluminum crap, but some are 3/4" steel crap.The 1/2" GI grip bar can be installed on the semi, but the barrel needs to be removed to do so.You are switching barrels, so might as well get it done right; special barrel tools and knowledge are absolutely required.Dan "Deerslayer" Block, mentioned above, and found in the pinned section, can do all of this Link to comment Share on other sites More sharing options...
peter kohler Posted June 23, 2019 Report Share Posted June 23, 2019 my 1975 wh has the modified mag catch, 1/2 inch grip rest, 10.5 smooth barrel with comp , ez pull springs removable stock and selector switch for holding the bolt back for easy installation and removal of the drum. I also have a khar 27 built exactly the same but with a finned quick change barrel and the removable stock has the sling swivel mounted on top as per the british modification. all these mods were done by dan block. the modified mag catch allows me to use un modified usgi mags which are expensive and have their own historical value I would suggest talking to dan about these mods. 1 Link to comment Share on other sites More sharing options...
tbirdsc Posted June 23, 2019 Author Report Share Posted June 23, 2019 Hi AllThanks for the infoI have been slowly but surely going thru all the posts - I wish I would have started this project when we had two feed of snow on the ground.I have one more question before I start pondering which direction to go with the mods while my paperwork is being processed.On the horizontal forend - just by looking at the smooth and finned barrels profiles on pictures - it looks like the finned barrels are a larger diameter - so are the forends milled for the smooth barrels and need to be altered for for the finned barrels or are they milled for the finned barrels and then there is a gap for the smooth barrels?Thanks again Link to comment Share on other sites More sharing options...
Hossbreed45 Posted June 23, 2019 Report Share Posted June 23, 2019 I'm no expert here by any means but I believe that the O.D of both finned and smooth barrels are the same diameter where it meets the receiver, therefore a GI handguard that fits the 1/2" wide grip mount will work for either barrel. There is no difference. The commercial handguard with the 3/4" groove will work too but there will be a large gap between it and the barrel. Just won't look right! Experts may correct me... Link to comment Share on other sites More sharing options...
06AngusSG Posted June 23, 2019 Report Share Posted June 23, 2019 GI spec barrels, bother finned and smooth, have the same shape profile. Kahr and West Hurley barrels also share a similar profile. However, GI spec and Kahr/WH spec are totally different. The Semi auto barrels are a larger diameter and have a longer taper to try to make the long barrel not look as bad. If you get a GI spec make sure to get a GI spec foregrip or you will have a large gap between the barrel and wood. Jon Link to comment Share on other sites More sharing options...
tbirdsc Posted June 23, 2019 Author Report Share Posted June 23, 2019 Thanks againSo are the WH/Kahr 10.5/SBR barrels GI spec or just a shortened version of their 16 barrels Link to comment Share on other sites More sharing options...
tbirdsc Posted June 23, 2019 Author Report Share Posted June 23, 2019 Also - was the grip mount bar always 1/2", I would have thought of leaving the bar 3/4" wide and eliminating the machining to step down to 1/2" would have been part of the cost cutting efforts done on the M1/M1A1? Link to comment Share on other sites More sharing options...
06AngusSG Posted June 23, 2019 Report Share Posted June 23, 2019 (edited) I'm not sure if the Kahr 10.5's match GI for specs but I do know that I've seen a lot of bad review about them. Better off with Green Mt, Richardson, ThompsonBarrels.com or a GI barrel.Grip hangers on all WWII Thompsons and earlier were 1/2" machined from solid stock. The 3/4" was introduced by West Hurley and continued by Kahr. They range from solid to a 2 piece stamped and welded. Garbage if you ask me... Edited June 23, 2019 by 06AngusSG Link to comment Share on other sites More sharing options...
tbirdsc Posted June 24, 2019 Author Report Share Posted June 24, 2019 OK - thanksI misread the Numrich description on the forends with the 3/4 slot as NOS for USGI when it was NOS for WH units hence the question about the width on M1 grip bars - just been over absorbed on all the info I have been researching. Link to comment Share on other sites More sharing options...
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