An */technical reloading question

bassassassin007

I just started handloading a few months ago, and I only load .308 and 7mm Rem Mag. I started trimming the cases to 2.005 and 2.490 respectively. However because rim thickness doesn't seem to be consistent from one round to the next in each caliber I seem to have a small problem, over all length isn't consistent from one round to the next even though my trimmer trims the rest of the case to the same length from round to round. Consequently I am always removing the case, measuring it then reinserting and fine trimming to get consistent case length. If I didn't remeasure and retrim them, the cases would only vary a few thousanths of an inch from one to the next. That being said I still seat the bullets to the same OAL, 2.800 and 3.250.

I guess my question is this, does the extra effort of measuring, reinserting, and retrimming have any bearing on how accurate the cartridges will be or should I not worry about the few thousanths of an inch?

Thanks, Dave

Tailgunner1954

The reason for trimming is to make sure that the mouth of the case does not go past the recess cut for it in the chamber (If it does, the neck will pinch the bullet and cause a major pressure excursion).
Thumb rule on trim length is the the "minimum length spec" is .010 shorter than the "trim to length" which is .010 shorter than the "max length" spec (handy to remember if your manual dosen't list all of them).
For all practical intents and purposes, as long as your cases are between the min and max specs, you don't need to trim at all.
Will having them all the same make a difference? well if you and your rifle consistantly shoot in the .2's, than you might be able to tell the difference between long necks and short necks.

dcloco

Tailgunner has it right on the money.

Also, unless you are benchresting or have a custom chamber, trim your cases to the same length.

I check all new cases to make sure none are over max length. Fire all cases, clean, size/deprime, and trim. I measure all of the cases. Approximately 4-5% of the 100 cases, will still be shorter than recommended "trim to" length. Leave them alone, these will be your barrel fouling cases.

Trim to length all the rest, inside/outside chamfer the necks, clean the primer pocket. If you choose, you can debur the inside of the flash hole and depth size the primer pocket (not necessary for most people & rifles).

I clean my brass again....this time in clean, fine corn cob media. Clean brass = clean rifle.

Highball

quote:because rim thickness doesn't seem to be consistent from one round to the next in each caliber I seem to have a small problem, over all length isn't consistent from
Exactly how are you measuring your cases ? A caliper, measuring from base-to-case mouth..? Even if the rim was 1/2 thick, the overall length ought to be consistant.

Sounds like you perhaps need to refine your tecnique. Place the case in the trimmer and trim to length..then SLIGHTLY release the case and make a half-turn..retighten and take a few more strokes. Some trimmers will not trim the mouth precisely square..and the half-turn will take up the slack. Try it and see if that works for you.

dcloco

Forgot to ask...brand of trimmer? Model?

Some, you have to work at...to get a good, clean, straight, and to correct length of case.

bassassassin007

For the OAL they are being measured with a vernier caliper from the base to the case mouth. The trimmer is a Hornady cam-lock. When the case is inserted in the shell holder the measurements are essentialy made from the head of the cartridge. So if these measurements are all the same from the head, but the rim thickness varies, the overall length will by off. If I am wrong someone please straighten me out.

Dave

dcloco

I use the cam lock as well. VERY dissappointed, at first.

#1 - MUST use the Hornady shell holders. THAT is total BS of Hornady to force this issue. I drilled some old shell holders to fit (just have to drill the center).

#2 - need to be consistent on how tight/loose that you have the cam lock, everytime.

#3 - lube that puppy. Both sides of the cutting shaft, center oil well on the right stand, AND, make sure you oil the face of the right stand - where the fine adjust bottoms against.

This would be a great design, if they would put a hardened surface on the right stand for the fine adjustment to bottom against.

Highball

I use the RCBS trimmers...and they use a collet and grab the base.
Therefore..what you are describing is a charateristic of the Hornady..and may be unsolvable.
Using a shell holder and cam behind sounds like a receipt for indifferent oal....
Sorta like the Dillon trimmer (electric) that I spent a hundred bucks on..only to find .003-.006 differences in OAL of the cases.
Called Dillon to ask..and was told that "That was within the tolerences"...I wern't happy at all.....

dtknowles

If you are crimping the bullets then case length is critical for consistent crimp. If you do not crimp then as long as the cases are not too long you will be fine and accuracy difference very minor.

Tim

dcloco

Case length is critical if you partial length size, neck, or collet size.

Shorter case versus longer cases provides difference in the amount of hold the case has on the bullet.

Just work with your Hornady a bit...you will get it.

Make sure everything is lube. I highly recommend full sythetic, semi sythetic, or Dexron II or III transmission fluid for lubing the trimmer. Full and semi synthetic have great "cling" factor. In a pinch, the Dexron II or III have higher pressure rating AND lubricity than standard motor oil. If possible, mix up some trans fluid and either of the sythetics. Don't kid yourself, there is a little pressure on the shaft of the cutter. (no lube on the cutter edges/flutes)

I have a Forster, that rocks. But, it was used, looked ok, and performed ok. After I cleaned everything, lubed everything, then worked with it a bit, everything fell into place.

Highball - the "cam" is in the threads holding the cam lock. It should be the same, everytime, but the middle support, that passes through the shell holder, bottoms on the case. So, you have threads that provide an interference fit when the center support bottoms against the shell.

If the shells have high, medium, or low profile caliber/maker stampings, you have a difference. Difference in base thickness, another possible error in case length....etc, etc.

dtknowles

I said the accuracy difference is very minor. This is subjective and may not be minor to everyone. When you shoot with case necks that have some variation and you see vertical shot stringing in the groups is could be the bullet gripping force. Tighter grip on the bullet causes a faster pressure rise and greater pressure time trace.

Tim

dcloco

dt - agreed. Just wanted to point out the other attributes as well.

dtknowles

dc - I was just trying to let people know how to see if their accuracy was affected (vertical shot stringing). You were helpful in pointing out how to get the trimmer working better.

Tim

dcloco

I hear ya bro!

In my case, it is the SAME loose nut behind the keyboard AND the scope!