Home Forums Reloading Big Game Rifles ????Pressure Signs????

Occasionally I have trouble opening the bolt on my gun after firing. I have been full length resizing. The primmers are slightly flattening as well. I have tried numerous recipes with not a great deal of luck. Mostly seating bullets .010 off the lands. Its a 1:11 twist 23" Kimber Super America. I have been shooting 5 and then cleaning. Bottom metal screws are 40 inch pounds.

What is your recipe?

1. If you have no trouble closing the bolt and do have trouble opening it, the pressure is too high. How you size only has relevance if you're having trouble closing the bolt.

2. Primers are always flattened to some extent.

3. How far you seat the bullets off the lands probably has not much to do with your problem. I have never measured the torque on bottom metal screws on any gun I've ever owned; it's unlikely that has anything to do with it.

4. Some guns shoot better a little fouled. Your shooting 5 and then cleaning may be your problem. Try shooting 3 fouling shots and then shoot some groups. Then, depending on your gun, you may need to clean after every 20 to 100 rounds (really). If your last coat after cleaning is oil, stop doing that.

5. You might disclose what powders, bullets, etc. you have tried. It's unlikely that a 308 Winchester of good quality won't shoot well with IMR 4064 and decent (maybe even indecent) 165/168 grain bullets.

Make sure your brass is trimmed to factory spec length.
Measure diameter of necks of loaded and fired brass and compare, the necks on the fired cases should be .005 or so larger.
Size your brass so the bolt closes with a bit of resistance, if you set the shoulder back you are creating too much headspace.
Are you getting shiny spots near the head stamp where the brass is flowing into the extractor groove?
Load data would be helpful.

I would measure your case neck thickness of your brass. It may be as simple as turning the case necks to bring them down a thousandth or so.

Pushing the shoulder back too far (.002" +) is usually the cause of primer flattening. The case moves forward upon primer strike/ignition, the case grips the walls, the internal pressure pushes the primer back to the bolt face, the case head pushes back to the bolt face flattening the edges of the primer



limit your case movement by pushing the shoulder back a minimal amount

.010" is too close unless you have absolute control over seating depth. Seating depth can vary +-.005" depending upon how you sort your bullets and how well you control your seating pressure. i.e. your press has linkages that compress and back pressure from seating pressure can lengthen you CBTO (case base to ogive). Conversely, a bullet that seats easier than others can be seated deeper.

You can minimize the pressure variances by moving further from the lands which decreases pressure



If you are seating .030" or .060" off the lands then +-.005" CBTO measurements will not cause problems like seating close to the lands

1. You don't need to size the brass so the bolt closes with a little resistance. In fact, if you do so, your ammunition may not fit another gun (if that matters to you) and if you try that trick in a semiauto with a free floating firing pin you can get slam fires.

2. He is having trouble opening the bolt AFTER firing. If you chamber a case that's a little too big you'll have trouble closing the bolt. If the pressure is OK you will have NO problem opening the bolt after firing.

3. Unless the rifle has a tight custom chamber or brass is being sized down quite a bit from a larger caliber there is NO need to turn necks. In loading thousands of rounds among probably 40+ guns I have never been forced to turn down a neck.

4. A primer is always flattened to some extent. For large rifle primers (small rifle are different), if the primer is flattened clear out to the edge of the primer pocket, the pressure is at or mabe over maximum. If there is a little radius at the edge of the primer, pressure is probably OK at least for a strong bolt action gun (maybe not with other action types). A case that is sized too much will lead to head separations but not to excess primer flattening.

5. Seating a bullet against the lands is common in bench rest shooting. There is nothing wrong with it as long as the load is adjusted accordingly. That said, some guns/bullets shoot better with the bullet a bit off the lands.

6. When a cartridge is fired, the case gets shorter; never longer. Irrespective of what the official trim length is, if a cartridge will chamber easily, nothing is too long. That said, I trim when the sized case length is over what is said to be the maximum SAAMI case length.

Gentlemen,

Thank You All for your input!

Woods-I love the details!

I took this project(.300WSM) on for a friend! This was a new gun. The scope/base was mounted by someone else! The stock was replaced with a Boyd laminated thumb hole! When I started the stock was bowed out bad enough to have a lot of pressure on the bbl. I immediately tore it down to open the bbl channel and enlarge the recoil lug recess! I bedded with Devcon. There is no more touching or movement of the action in the stock! I torqued the both bottom metal screws to 40inlbs. In my screwball way of thinking, I was trying to break and determine the ideal load for this rifle. Looking back, I should have focused on bbl break in, only! I have used 180 Nosler BT,Hornady 165 Interlock, Nosler 165 and 180 Partitions pushed by a myriad of powders!
First: FL sized new Nosler brass. I loaded (5) 5-round recipes with the best one shooting .750" at 100yd! It was the second group shot. I was thinking, "I am the man"......(5) groups later, it turned to, "I am a moron"!
Mistake 1: Using a Lee FL die with a Redding shell holder and not measuring the setback. Due to the thickness of the shell holder, I was setting back .004"! The bolt closed firmly, but that did not concern me much at first.I was also pushing the bullets out to .002 to the lands. At 61 to 64gr IMR-4350, I was following my printed manual. The bolt got hard to open after firing! I also had the "shinny spot" on the head-stamp!
Mistake 2: Not rechecking/re-tightening the bottom metal screws!
Mistake 3: Assuming the scope rings were torqued to specs.
Mistake 4: Trying too many powders even though the were recomended. I tried: RL-16,Varget, Win760 etc.....

Good News.....everything snugged,torqued and lock-tited(blue) down!

It is shooting .750 with 64gr IMR-4350 and Nosler CT(Black) 180gr bullets!This is hunting gun and that's all it will ever be!You have to understand, this gun leaves in a few weeks to Africa to kill thinner skinned animals! So I have been pulling my hair out while under pressure to make it shoot decent! His goal is to shoot no more than 200yds!

Well, its off to the next conbooberated project!

I'm sorry this response got so long but, I felt I owed those of you that tried to help! Thanks again!

God Bless!

Brett

Glad you got it sorted out.

Woods,

I have been thinking! As we adjust our bullets to meet the lands, the pressure can either go up or down! So then, does the velocity change with different pressures?

I do not own a chronograph, I would like to buy an economical unit that will meet my needs! What is the best bang for the buck?


Thanks,

Grum,


From your words, are you saying that you trim your brass prior to resizing?

thanks,

B King

You'd be hard pressed to beat a ProChrono Digital in "best bang for the buck". They run about $100 from places like Midway, and are a big advancement from the old Shooting Chrony units for about the same money.

Also, yes, if pressure goes up, velocity will go up, although not necessarily in a linear manner. You can encounter pressure spikes that don't increase velocity as much as you'd expect.

Hope that helps.

Yes, velocity will be effected by seating depth

For example here is a seating depth test



Note the velocity goes down incrementally with deeper seating depth. What I look for is the lowest ES & SD along with good accuracy and chose the .060" off the lands for this rifle.

I second Yondering on the Pro Chrono, much better than the Shooting Chrony and economical