Firing pin hole to large?

[gunderwood]

The manufacturer told me this is fine, but I'm not quite sure.

The rifle is a DTA SRS. I have the .308 and .338 bolts. I have shot lots of rounds through the .308 and only get primer flow when I push the pressure. This is what I expect. However, on the .338LM I get primer flow every time. Nothing else says excess pressure though. Head expansion is 0.001" (and this is new brass, so some growth is expected). No ejector swipes, headspace is fine, etc.

Here are the reload info:

New Lapua brass, Fed 215M, Lapua 300gr Scenar 0.010" jump and either 82gr RL-25 or 87gr H1000. The H1000 load is a little hotter than the RL-25, but neither should be causing primer flow.

I took the bolts apart and measured the firing pin holes thinking there may be too much clearance. Both firing pins measure 0.064", but the .308 hole measures 0.070" while the .338 measures 0.080". 0.006" for clearance on the .308 sounds fine for a field gun, but 0.016" is too much IMHO. The primer flows I am getting are very minor and measure approx. 0.080-0.085". The bolts are more or less identical except the ejectors and bolt face.

DTA told me that the firing pin floats so it wouldn't matter, but I don't buy that. The pin doesn't float until you re-cock the bolt after firing. The firing pin dent in the primer isn't caving in either, which suggests that it is supported during firing.

Besides the hole being too large, the only other thing I can think of is the firing pin spring is too strong. I am going to set off just a primer to see if there is any flow or not. Other ideas?

<span style="font-weight: bold">Edit:</span> I should note that I have loaded the same lot/100 pack of primers in .300WSM and that gun doesn't have primer flow despite a max load. I don't think it is the primers being too soft, but the other gun is a BAT action so tolerances are probably tighter.

 

[Greg Langelius *]

Re: Firing pin hole to large?

As long as the other pressure signs are nominal, and the primers themselves are not suffering any kind of failures, the worst case scenario is that one of your pressure indicators is maybe less reliable.

Personally, primer cratering is only one of several indicators I pay attention to; including primer edge flat/sharpening, bolt lift effort, and case base burnishing. Taken by itself, I'd be less concerned with it than when it is accompanied by other signs.

Greg

 

[gunderwood]

Re: Firing pin hole to large?

I've just never had a rifle that would do it every time. Don't want to work a load up an in the process, before other pressure signs are evident, rupture a primer on nearly 90gr of powder. Probably wouldn't be too pleasant.

 

[Greg Langelius *]

Re: Firing pin hole to large?

I have blown primers clear out of the pockets on 40gr of powder.

Not fun. Usually disables the bolt (ejector/extractor damage)

 

[Unsichtbar]

Re: Firing pin hole to large?

My DTA SRS .308 does have what would be call a crater on each round fired ( so does my AIAW ) regardless of how hot the load, no other preasure signs. I use Russian Magnum Primers ( harder cup material not more primer mixture)they helps counter the formation of the crater.

 

[DBohn]

Re: Firing pin hole to large?

Gunderwood,
I have the same issue with my DTA SRS with the .338 Lapua Mag barrel. I've been working so much lately I've only had a chance to take it out once and during that outing performed a ladder test.

New Lapua Brass, 300 gr. Scenar .010" off lands, CCI 250 LRM primers and VV N170 powder.

I experienced the same primer flow on every round ranging from 82.0 grains of N170 up to 90.0 grains in 1 grain increments and from 90.5 to 92.0 grains in .5 grain increments. 90.4 is VV's max for the 300 gr. matchking (they don't list the scenar). Even with the 92 grain load I still don't have any signs of pressure like flattened primers or sticky bolt and like I said the primer strikes look identical to the lesser loads. Doesn't seem to be much of an issue but getting the bolt bushed by a competent gunsmith would probably clear it up if you wanted it fixed.

 

[Hummer]

Re: Firing pin hole to large?

The larger striker opening is way oversize. I like my strikers to have about .003" clearance on the few occasions I have bushed a bolt face.

 

[gunderwood]

Re: Firing pin hole to large?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">The larger striker opening is way oversize. I like my strikers to have about .003" clearance on the few occasions I have bushed a bolt face. </div></div>

I don't understand how this would close up the opening? I've never had a bolt brushed, what exactly is it?

 

[DBohn]

Re: Firing pin hole to large?

This explains what it is and goes into detail on the process.

www.bordenrifles.com/firing_pin_bush.pdf

 

[Hummer]

Re: Firing pin hole to large?

That is essentially what I do except I mount my bolts in a fixture similar to a LaBounty and plunge a 1/4" end mill into the bolt face after truing the bolt body to run dead center.

I plunge it in about .175" leaving a flat bottom. I then turn a cylinder (from 1/4" drill rod stock) that has a very slight taper at bottom side and slightly larger on bolt face end. Say .249" to .251" so it will get snug just as soon as it starts in hole.

I cut it off at about .190" long and measure the striker nose diameter and then find the drill that is just under the nose diameter and after starting hole with 1/8" center drill I ease in the small drill till it goes through and try the striker. It should be snug. Then I use the next size drill up which is about .002" larger and drill it. Striker then goes in and out freely.

Take it out of chuck and check it on striker nose to insure there is enough clearance for the striker to protrude throughthe hole about .060" and then start the tapered plug into hole in bolt face where it should immediately get tight and not go in. Next I take it to arbor press and align bolt vertically and with a small cylinder on the top to align the back end of the plug I ease it in with the arbor press for a interference fit.

Rechuck the bolt back in fixture and with small carbide boring bar I do skim cuts till the plug is flush with the bolt face.

I have seen a fair amount of bolt faces that have gas cuts around edge of primer from guys trying to get too many reloads out of their brass or from cup failure. Large primers are .210 so the gas cut ring is say .210 to .215 in diameter. Making the plug .250 cleans it all up.

Model 70 bolts are somewhat soft and easy to plunge cut. I have seen them develop egg shape striker openings. The drill rod is a tougher steel and I have yet to have a bushing show elongation.
The worst bolt I ever did was a 1903 Springfield bolt. That sucker did not want to cooperate at all as the bolt face was hard.

I have not had a bushing set in deeper as the 3 ton arbor press makes sure it is bottomed out on the shelf left by the milling cutter. Never had one get loose either as it is a force fit.

I have also changed out bolts/strikers on Pattern 14 enfields. They are notorius for puncturing primers. The Pattern 14 striker is way too sharp so I change the striker for a 1917 striker which is around .062" and drill the hole as above.

The WW1 field ordnance kits supplied two size strikers. One for the Pattern 14 and one for the 1917 so the ordnance types could repair a Brit or US rifle.

 

[gunderwood]

Re: Firing pin hole to large?

For a field gun I won't push pressure like benchrest does, but getting primer flow is a problem. When the round is ejected, a little bit of that flow can get broken off and end up in the firing pin assembly. If this happens it can cause light firing pin strikes. I had it happen when I ran the max pressure test for the .308Win barrel in this gun. I had to clean out the firing pin assembly before it would shoot again.

On guns this expensive I don't think I should have to brush a bolt. The tolerances should be held tighter from the factory. I guess that isn't the norm from the replies so far and not just from DTA. I expected those kind of tolerance swings with a stock Remington or something, but anything over 2-3k it shouldn't be an issue, IMHO.

 

[Hummer]

Re: Firing pin hole to large?

All bets are off any more on choosing a gun by the name on the action and it being a fine specimen.
Several years ago I bought two new rifles for Christmas. Both had to go back to their respective manufacturers. One had insufficient striker energy and the other not only had that but excessive headspace.
I have seen new guns with crooked bores and many are known to have threads in their action that are not at right angles to the bore line resulting in off center striker hits and harmonic problems.
A guy I once worked with said it best. "A new rifle is like buying a kit that has to be reworked to make it work."

I watched the US Border Patrol Gunsmith take three new 700 Remington Varmints and he went out and tested them with Fed Match for initial accuracy groups, then he came back and pulled the barrels off, squared the front of the receiver, squared the lug shoulders, recrowned the barrel, cut a thread off back of the barrel and rechambered to min headspace, put a 11 deg crown on it, free floated the barrel channel, bedded the action after adjusting the triggers and restested with same ammo and all three shot groups at least 1/2" smaller than originally.

Manson Precision Reamers makes an action truing kit that does a good job of reworking an action to make it better. My buddy who retired as Chief Armorer from the Secret Service who built all their sniper rifles came down a number of years back and built two rifles while he was here and I watched him take a Manson kit and true a Remington action. After he did so we shot it and he looked at primer of the fired case and he said it was far more centered than when he first shot it as he had trued the threads and front of the action. Dave also makes a kit for Winchester 70s and I don't know who else.

Guys that are hired by gun companies are not (contrary to popular belief) descendents of John Browning, Sam Colt etc but any jerk they can find to do a job. I was at Colt on one of my business visits and I was walking around and I watched this guy making a M16 part and I asked him what he was making and he said he did not know. They have to hire literally anyone that walks in the door.

I was over at a Sportsmans Warehouse a couple months back and I looked at three Remington Varmint rifles in several configurations and all three had wondering bores and I left them.

Had a friend get a top name barrel for his 1000 yard rifle. I chucked in it lathe and dialed it in and turned lathe on and looked down the barrel while it turned. It was enough to get you drunk. I called him and the company that made the barrel. They sent me a new barrel no charge and said keep the other one for a hunting rifle. It is 28" now and I suspect I will have to cut 10" off the muzzle to get to the straight section.
Get Hinnant's book on THE COMPLETE ILLUSTRATED GUIDE TO PRECISION RIFLE BARREL FITTING. This will explain in detail what needs to be done.