Mini 14/M1A Hammer spring tension

[jlmurphy]

I have a heavy barreled Mini 14, it normally shoots nice small groups. In an attempt to improve ignition, I increased the hammer spring tension. Instead of smaller, my groups were three times larger. At the range I tried single loading, mag in, mag out and determined that bolt position was the problem. I think the increased hammer force is disrupting the bolt at ignition. I will reduce the spring tension and try again, but was wondering if anyone else had this experience? I know that the M1A, Garand and Mini 14 all share similar bolts.

 

[Winger Ed.]

That's a headscratcher....

However; I doubt if the hammer spring is the problem.
Its unrelated to the bolt's positioning. The only thing I can imagine causing the bolt to not close all the way is that the grooves the operating rod travels in are dirty, the bolt has some grud on it, or the chamber might be dirty, and the spring can't get enough 'omphh' to slam home the operating rod & finish closing the bolt.

A stronger hammer spring won't upset the bolt, it will just speed up the 'lock time' between trigger pull and detonation of the primer........ which should help shrink your groups.
That's what speedlock Titanium firing pins and after market spring kits are all about.


I'd clean it real, real well, make sure the stock/action, all that is put back together properly, and maybe try some different ammo.

.

 

[jlmurphy]

My intent was to speed lock time and improve ignition, and on a bolt gun it is easier, the bolt is much heavier and fit more closely. On this type of semi auto the bolt is much lighter, the rear is not as controlled, and the hammer after striking the floating pin finishes against the bolt body. There is also a bevel cut on the bolt that corresponds to a protrusion on the hammer to prevent the hammer from contacting the pin until in battery. Everything is clean, the chamber is tight, the operating rod is completely closed. I think the bolt is being knocked forward a few thousandths and reseating on ignition, which opens up many variables. I'll try again today.

 

[Winger Ed.]

Naturally,
I wish ya the best, and I'm very familiar with both mini, and M-14 rifles.

But, If the rear of the bolt is anywhere near the hammer when it falls,,, the primer & round is going to fire. That's all it can do.

Sure, there is some slack in the (closed)bolt, but if its within spec. for the headspace, and you're not blowing out the back end of a brass when it fires, that bit of movement is almost irrevelevant to the strength of the hammer spring.

.

 

[Jim K]

Consider that when the hammer spring (mainspring) drives the hammer forward, and the hammer contacts the bolt, the bolt is also driven forward. This affects (to a small amount) the headspace as well as possibly the position of the powder in the case. The firing pin blow will also be stronger, and ignition will be affected. All those factors can definitely affect accuracy.

Does anyone ever think that the designers of a firearm just might have known what they were doing?

Jim