Bolt close tension

[Randyc]

Hey guys and gurus of the barrel nut,
question,
how much bolt close tension is normal?
from empty chamber to factory ammo to handloads FL sized?
or what factors affect bolt closure resistance?

[Robinhood]

Cocking force is mostly discussed on the opening side where the cocking pin runs up the ramp and sets in the pocket, Fred Moreo introduced us to many of the timing issues with savage actions. To answer your question the lug ramps and the process where there is a hand off between the sear and the trigger, part of the timing process that involves the cocking ramp transition area as well as the gap between the sear and the trigger mating surfaces.

If I missed it or did not explain it correctly someone please set the record straight.

[Hotolds442]

It should close quite easily, like using just your pinky. If not, the first 4 things that come to mind as far as closing tension goes, are the distance from the bolt face to the barrel, the bolt face to the case shoulder, the length and diameter of the case neck, and the relationship between the bullet bearing surface and the rifling lands.

If if the chamber is reamed too deeply, the bolt face could be dragging on the breechface which would add resistance to closing. In the second example, a case that is too long from base to shoulder would need to be "crushed" in order to close the bolt. In the third case, the long neck would be shoved into the throat of the rifle, effectively crimping the neck on the bullet during closing while a thick neck would need to be forced in adding neck tension, and fourth - shoving the bullet into the lands during closing. Most of those issues can be seen either with the naked eye or by smoking the bullet, neck and shoulder over a candle.

Im sure there are more I've overlooked. Like a front action screw that's too long.....

[Randyc]

Thanks guys for the reply, as always great info on here.
I have put much thought into something to "see" where the case and bullet is making contact. Hadn't came up with "smoking" over a candle. That is a great idea and might help explain what's going on. I am using Hornady virgin brass.
My build,
savage 12 single feed
7mm08 custom barrel (trying a bison gun works )
Berger 168 VLD'S
set hesdspace at app. .004
i am using a dummy round to get OAL
have some factory Federal Fusion 140's
all add some "weight " to the closing force.
Handloads seem to have more weight than the factory.
Hornady brass has been tried out of box and FL sized. Same result.
I will use the smoke and see where I am, will get back with you guys tomorrow.

[Randyc]

Should it close as easily on a round as it does with no round in chamber?

[Hotolds442]

Almost as easily.

If you close the bolt on an empty chamber, with the rifle already cocked (firing pin not protruding) and then open it, does it also open hard?

[Hotolds442]

I wonder how many chambers have been cut on Bison's reamer.....

You'll find the problem, just add smoke.

[Randyc]

Checked empty chamber close again,
compared it to factory round,
Went back to reloading manual to double check case length, MAX is 2.035- out of the box, Hornady is 2.030- case in point for the example was used in a savage 12VSS, trimmed to 2.025. I sized and trimmed a case to the 2.025, no bullet, tried it and same thing, has about two times the tension as an empty chamber.

All atempts were with the trigger cocked and safety in on position. Bolt lift is easy up to the cocking point of travel.
You guys mentioned flaws in the bolt and cocking mechanism, what can be done to help these flaws?

[Randyc]

Would a small base die set make a difference?

[Randyc]

Smoke showed me the problem, I can't post a pic , but the base (big side toward the primer end of case) of the shoulder is touching the throat. The very tip end or edge.
Can this be tight headspace?
i am pretty confident the headspace is .004

[Hotolds442]

If you're talking about the junction between the case body and shoulder, that's usually caused by a seating die that's set too deep.
Run a case through your sizing die, leave the bullet out of it, smoke it, and see how the bolt closes on it.

[Robinhood]

Can you describe the process for checking head space. You are confident of the .004, how did you arrive at this number?

[Randyc]

I used a Forster go gauge with a piece of .004 tape on the base for a no go. Bolt closes easily on go, will not on the no go. Very clear difference.

[jonesturf]

So just to be clear it's only happening when there is a round and not on an empty chamber? Sounds like a headspace problem if that's the case. Pickup a set of the Hornady headspace gages that measure off your shoulder and attach to calipers.

[Robinhood]

So just to be clear it's only happening when there is a round and not on an empty chamber? Sounds like a headspace problem if that's the case. Pickup a set of the Hornady headspace gages that measure off your shoulder and attach to calipers.

Yep

[jonesturf]

You need a way to measure the headspace of your brass. Either grab one of those sets or in a pinch I've even used nine millimeter brass. As long as you use the same one each time it should be pretty accurate. Fire a round and measure that and then adjust your sizing die to bump 2 thousands of an inch. You should be good to go. If not then there are other issues with your chamber or brass but, hopefully not

[Robinhood]

That will work. Compare your sized brass to your head space gauge. You could also just make minor adjustments in your die on one piece of brass until it fits being your head space is set correctly..

[jonesturf]

That's another way too. I just recommend using gages and getting actual measurements because its hard to tell how much you're actually adjusting. You don't want to be sizing too much and run the risk of stretching your brass so much after 3 firings your case heads are separating. Just adjust in very small increments. Every 5 degrees of rotation gets you about .001" change in the shoulder length (headspace). You shouldn't need more than 2 or 3 thou or you're doing too much.

[Hotolds442]

Do the 9mm trick on both your go gauge and your unfired brass. The brass should be shorter. You would not be the first guy this week to have a bad headspace gauge from the manufacturer.
Since it's also occurring with factory loads, it sounds like your headspace is a bit tight. You could easily set your headspace to the factory loads and be on your way.
The barrel is threaded at 20 threads per inch. One full turn of the barrel is equal to .050". 7.5 degrees of barrel rotation is equal to .001, so 15 degrees would be .002", etc.

[jonesturf]

The barrel is threaded at 20 threads per inch. One full turn of the barrel is equal to .050". 7.5 degrees of barrel rotation is equal to .001, so 15 degrees would be .002", etc.

I was talking about setting up reloading dies which are 14 tpi.