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jerhelo
10-30-16, 13:12
Saw this when I installed the magpul SGA stock on my mossberg 590a1. The stock screw on the factory stock doesn't use all the threads either but the SGA stock screw from magpul actually uses one less thread even. Not sure why they did not elect to go with a slightly longer screw and use all of the available threads considering that this is an aluminum receiver.

If you take you trigger assembly out and look at the back of the threads you can see what I am talking about. I am probably over thinking this but actually picked up a few longer screws to install, it is a 5/16" x 18 allen head available just about anywhere. I think the 7/8" would have been a better choice.
GH41
10-30-16, 14:26
You are right about one thing.. You are overthinking it. Basic rule without looking in the book is twice the diameter depth in soft metals is the max needed. Another thing to consider is the receiver may not be threaded through. Run a longer bolt in (without the stock) to check thread depth. Whatever you do don't use a stainless bolt! SS and aluminum do NOT like each other. Also be careful with liquid threadlockers. Some plastics don't like them.
jerhelo
10-31-16, 05:56
Great points, I don't think there is enough thread to get twice the diameter in depth. In fact it appears that less than a 1/4" of thread is actually being used, that why I was thinking about increasing the thread length another 1/8". There seems to be enough thread to do that. Magpul recommends blue lock tight in other discussions so I would assume their plastic is fine with it. Just seems like a high stress area of the gun to not use as much thread as possible.
GH41
10-31-16, 15:45
My SGA is on an 870 and the cap screw probably threads 3/4 inch into the steel lug on the receiver. I too would want more than 1/4" into aluminum. For the price of a new screw another 8th would be cheap insurance.
williejc
11-03-16, 06:07
The 590a1 receiver is steel, not aluminum. However, the 590 receiver is aluminum.
BBossman
11-03-16, 07:24
The 590a1 receiver is steel, not aluminum. However, the 590 receiver is aluminum.

Actually not, they both use an aluminum receiver. The A1 uses an alloy trigger housing, whereas the 590 uses polymer.
L-2
11-03-16, 09:55
Post #6 is correct.
Post #5 is in error.
williejc
11-03-16, 18:26
My error about 590a1 having a steel receiver. It and all other Mossberg 500 or 590 series have aluminum receivers. Thank you for correcting the misinformation.
jerhelo
11-05-16, 15:15
Exactly. Seems like a very small investment. Was literally $0.78!!!! Haven't gotten around to installing it but will soon.