Can Undersizing Cause Tight Bolt

[mikeeg02]

With that harrels (or anyones measuring device not made from the same reamer as yours) you're "assuming" their shoulder angle is exactly the same as the reamer that cut the chamber. It may not measure at the important part. Your chamber is your best measuring device.

Ideally you should make sure the piece of brass closes in the chamber of the gun smoothly. Measure that case and make that be the measurement you size to.

Especially with stout loads, this becomes all the more important.

If you've got a few firings on the cases and havent annealed, you generally have to adjust your die.

Just my two cents.

 

[spclark]

Case sizing die mismatched to chamber shape can throw you curves.

When sizing brass there're two dimensions that are critical: shoulder bump - often referred to as 'headspace', and the case body diameter just ahead of the extractor groove.

If your current die isn't sizing that second dimension properly your sized cases may expand too much upon firing, hence the sticky bolt sense you come away with.

(I admit I haven't read this entire thread so if I've missed something feel free to let me know.)

You may benefit from a custom-made die, cut to a profile taken off a few of your fired and UNsized cases. John Whidden, Neil Jones, others... can help you with this.

 

[gunsandgunsmithing]

Three things(generally) cause hard bolt lift, and shoulder bump ain't one of them.

1.)Lack of diametrical sizing
2.)Rough chamber
3.)Too much pressure

Only too much pressure will cause significant resistance to lifting the bolt from the very start of bolt lift. The other two create bolt "click" at near the top of bolt lift. The bolt does not begin moving rearward for several degrees of bolt rotation. So, unless the case is holding the case against the bolt face from excessive expansion longitudinally,(pressure) lift will not be heavier than normal at the start of bolt lift. Once the extraction cam surfaces come into contact with one another, breaking the tapered case free of the tapered chamber can happen but those cam surfaces do not come in contact for several degrees of rotation.

 

[mikeeg02]

Jim,

Also get yourself some of these or something similar to swab out your chamber before firing. Any even slight moisture that gets on the brass or in the chamber area will give stiff bolt lift. Ask the f class guys that have to shoot in the rain. Or if you take warm ammo out in the cold and moisture condenses on it. Try to keep as much moisture out of there as possible.


https://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-swabs/shop-swabs-prod564.aspx

 

[newbieshooter]

Mike
This extra effort lift was noticed during a cold weather first relay, others were experiencing the same thing.

I also shot the first relay at the same club match as @SPJ . Outside air temperature was about 29-30 degrees when relay one got started. What I noticed was that when i opened my ammo box (which traveled a while in a warm car/truck/van - then stayed in my carry case until match time) the cold air hits the 'warm' rounds and you'll see a thin layer on condensation form on the brass. If you shot these rounds with condensation on them - you can experience increased pressure and heavy bolt lift. I take a dry towel and give the rounds a good wipe prior to firing. After the rounds sat out for a while, the brass temperature soon matches the ambient air temperature and the condensation disappears.

It was noted that heavy bolt lift only seemed to occur on the first relay when shooting initially started. anyways - that's just my observation.....
J

 

[mikeeg02]

Three things(generally) cause hard bolt lift, and shoulder bump ain't one of them.

1.)Lack of diametrical sizing
2.)Rough chamber
3.)Too much pressure

Only too much pressure will cause significant resistance to lifting the bolt from the very start of bolt lift. The other two create bolt "click" at near the top of bolt lift. The bolt does not begin moving rearward for several degrees of bolt rotation. So, unless the case is holding the case against the bolt face from excessive expansion longitudinally,(pressure) lift will not be heavier than normal at the start of bolt lift. Once the extraction cam surfaces come into contact with one another, breaking the tapered case free of the tapered chamber can happen but those cam surfaces do not come in contact for several degrees of rotation.

If you're running a warm load, and you don't bump your shoulder back enough for there not to be any resistance when you close the bolt, I can assure you the bolt will be stiff to open. It took me a while to put the two together this summer, but since I started checking them in the chamber, all my stiff bolt issues went away. I dont typically anneal, so sizing becomes even more important. 90% of my brass was smooth on close and smooth to open. But occasionally I'd feel a little pressure on bolt close and those were the ones that were stiff to open. Not a clicker, but stiff to open. Plays hell on your record string.

 

[gunsandgunsmithing]

If you're running a warm load, and you don't bump your shoulder back enough for there not to be any resistance when you close the bolt, I can assure you the bolt will be stiff to open. It took me a while to put the two together this summer, but since I started checking them in the chamber, all my stiff bolt issues went away. I dont typically anneal, so sizing becomes even more important. 90% of my brass was smooth on close and smooth to open. But occasionally I'd feel a little pressure on bolt close and those were the ones that were stiff to open. Not a clicker, but stiff to open. Plays hell on your record string.

Tell that to P.O. Ackley or anyone who uses a slight crush fit of the case in the chamber while forming cases. Perhaps if you are wayy over crushing a case in the chamber, the brass will have no place to go, but under what I'd call normal circumstances, the 65K psi of firing the case will iron out any small crush fit issues, fireforming or not. The brass will flow to a happy place and then constrict back about a thou...releasing pressure on the bolt face and bolt lift is not hard. I've loaded a bunch of cases and I can't think of an instance where stiff bolt lift couldn't be traced to one of the three things I mentioned. Bottom line though...if the bolt lift is stiff at the start, there is pressure between the case and the bolt face. You just have to figure out how/why the case is not springing back enough to create a miniscule clearance..or at least a lack of pressure against the bolt face. I admit that his cases do appear to be tight upon closing and not suffering from a lot of pressure, based on the cases being "rubbed" on the bases and the primers look as though the pressure is mild. Perhaps he needs to go UP on pressure to "iron out" the tight initial fit....or maybe a combination of bumping a tad more and raising the pressure. What is the neck clearance? I ask because it might be tight enough that it leaves nowhere for the brass to go.
I stand by this point...if bolt lift is heavy from the start, the brass has not constricted to allow any amount of clearance, as it should and there is still a considerable amount f pressure from the case on the bolt face that shouldn't be there. Obviously, in the case of fireforming, there is a place for the "crushed" brass to go and bolt lift is easy even with a tight bolt closure.

 

[mikeeg02]

Crush fit for forming to a chamber when changing shoulder angle is a different circumstance. As I agree in that instance. I do it as well. Brass is also likely to be freshly annealed.

So I'll make the distinction.

With a formed case, with a warm load, and bolt resistance on close, you'll likely have stiff bolt lift. I think it's more noticeable with cases that have had a few firings on them since last annealed. As they lose their ability to spring back from fired size.

 

[mikeeg02]

I didnt notice a change in the way the primers looked in my case. Just false sense of pressure via intermittent stiff bolt lift. Fixed my bump by checking them in the chamber, no more feeling on close. No more bolt lift problems.

Though your experience could have been more moisture related, as other experienced as well. Or a combination of the two. But I would just be in the habit if checking a few in the chamber as you go through your cases. You must make sure your chamber is clean and no residue from solvents or anything else! Otherwise you could think you felt something and get messed up even further.