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A few thoughts. First, there are no substitutes for mass and rigidity. Vibration and flex are maddening, even when working on small projects. Look at the weight of the machines you are considering, along with the width of the dovetails where the table or head move. Second, avoid round...

I have long been taught that: 1. a properly-sized recoil spring will prevent a recoiling bolt from striking the back of the receiver; 2. if you want to use ammunition with a higher recoil impulse, you should also change the recoil spring to match that new ammo; and 3. as a recoil spring...

Interesting. I have only seen the large SERIAL NO. stamping on Fruithurst guns. Pure speculation, but I wonder if the tube portion of your gun was started in Fruithurst and then brought to Irvine where it was completed and numbered. Regardless of the reason, it seems there were a lot of...

Thanks. One more test of my data set if you do not mind. So far, on the S prefix guns I have seen: Guns up through number 138 have a 5-character serial number with the letters SO as a prefix followed by a 3-digit number - SOxxx. Gun with number 219 and higher have a 4-character serial number...

Montana - Not as early as yours, but early enough to have a stamped magazine housing with the stylized MKA logo on it. Based on your serial number range, I suspect your gun has a stamped magazine housing, but does not have the stylized MKA logo on that magazine housing. How good is that...

Montana: I am not sure. I suspect my Irvine is in the first half of production simply because it has a stamped magazine housing. The guns I have seen with a cast magazine housing appear to have higher serial numbers than those with a stamped housing. Is there a better test or a more precise...

Austin: Thanks for the info about the factory recoil spring guide in your video. Interesting that it is from a Fruithurst gun. It appears that this is one of the components that Mr. Ruplinger upgraded when he moved his operations to Irvine. My Irvine recoil spring guide has a machined back...

Austin: Nice video illustrating the multiple functions performed by the recoil spring guide, and nice workmanship on the recoil spring guide I got from you. The amateur engineering historian in me is intrigued by the MK Arms guide in your video. More specifically, I am trying to figure out...

I agree with ShureShot. Even before you head to the range, you might want to put a wrap of masking tape around the base of each magazine, number them, and leave enough room for notes about how each particular magazine performs. Your phone camera can also be a useful tool when it comes to...

The Dude – You may have already done this, but Scott Andrey has a Magazine Problems page describing how to troubleshoot a 76/760 magazine. He also includes hyperlinks to photos illustrating each part or step that he discusses. I found that if you take your time and go through each step of...

It did not feel like it was even close to pushing back the bolt. I had to push down on the back of the receiver to get the bolt to move back at all. As soon as I started to release that pressure, the bolt firmly pushed back all the way to the closed position. This is a factory MK Arms spring...

Slowmo – As an FYI, I just tried the weight-of-the-gun technique on a 760. It did not push the bolt back at all. It appears that technique only works on guns with a certain ratio between the weight of the gun and the strength of the spring. The 76/760 appears to be too far out from that...

This is proving to be a very educational thread for me. I have learned both new techniques and new things to consider when thinking about recoil springs.

As I recall, it was PK who headed up the effort to get the proper specs to Wolff to duplicate the factory recoil springs. The factory MK Arms springs have 60 coils, but the Wolff springs have only 58-1/2 coils. I wonder where Wolff got that number. Could the original S&W springs have been...

Thanks for the response. I have been using the same criteria for bolt travel that you describe, but have been measuring it in a more old-school manner, using masking tape over the cocking slot and observing how far back the tape is torn by the bolt handle during firing. This has served me well...

The recent discussions about spare parts got me to thinking about recoil springs. For many firearms, I see replacement intervals for recoil springs that are based on either: 1. round count (i.e. replace the spring after x number of rounds); or 2. length of the relaxed spring (i.e. replace the...

I agree that the extractor appears to protrude past the nose of the bolt. Based on the rub mark on the very front of the extractor, it looks like it like it protrudes so much that it strike the breech end of the barrel. How much front-to-back play is there between the extractor hook and the...

Deuce: I am not sure if I have said this before, but thanks for developing your innovative stock adapter - sturdy, no moving parts, no new fasteners, and no modifications to the gun itself. Another one of your inventions I would like to see come to market is the full-auto only sear that you...

A couple of thoughts from the peanut gallery here: It looks like you have two separate things going on here. On the first jam that occurs around the 12-second mark in your video, the fired case ejects nicely, but then it looks like the gun double feeds. Scott Andrey has a step-by-step procedure...

Can you post photos of the old and new extractor springs next to each other?