Rimfire rim thickness gauge.!!

[native hunter]

G"day All
Today I was at the range and on the look out for a once fired 222-223 case,Why you ask.??
Well i read on a forum somewhere they make a good rim thickness gauge so off i went and tried it out today.
As it turned out their was some 223 cases and they were to small in the neck and another bloke had some 222 cases,one was way to tight and the other was just perfect.
I came home and batched some eley black and was surprised to find the rims differed into 3-4 groups.
They varied as much as 4 thou.!!
As you can tell its just a matter of measuring the case and zeroing and then drop in the round and measure the rim thickness.!!
I end up with 2 full packets of batched ammo to try tonight.!!
Do you think the ammo with the thicker rim will give better results due to tighter head space.??
Regards
native

[Brett33]

Short answer no. In my opinion and from test results I have read as long as you have good ignition head space matters little. If you are to test to see if there is a differance do it blind otherwise you will get the result you want. Get somebody to code them batch a and Batch B without you knowing which is which, then check the results and report back.

Brett

[native hunter]

G"day All
Well the jury is in and no it made little difference tonight.
I shot a 199.14 on the business card and considering the club i shot at shoots off metal frame wood top benches with wheels on them its not a bad result,boy they move with the slightest body weight near them.!!!
I tried a different technique on a practice target and I shot worse,I thought if I rested my left arm on the table and hand on the speed screw it may steady it but the rebound was a killer.!!(197.11).
It was pretty tuff shootin off wooden benches and with a ribbon on a stick for flags.!!!
Anyway the search for perfection goes on and im lovin it.
Regards
Native

[SnipeWench]

NH,

Very interesting idea re the method of batching, though using a .222 or .223 case! I never thought of doing it that way!

I think the main reason for batching for weight and rim thickness is to provide a more consistent batch. If you're going into a major comp, and the brand of ammo is known for odd hotshots or rounds that _just_ make the target, batching should pick these up. After all, one point is often the difference between 1st and 6th.

If batching ammo means that you pick up one point, then it's prolly worth it.

It is _then_ up to you to place the shot in the centre of the target consistently.

To help you read the wind a bit better, and work out holdoffs, look at the chart on the BRT website: http://www.benchrest.com.au/tipsforbenc ... ooters.htm <-- this version approaches the problem by showing where the bullet will strike based on aiming dead centre on the target.

There is a slightly different version on the Rimfire Accuracy forum: http://www.rimfireaccuracy.com/Forums/s ... -I-made-up <-- This version approaches the same problem by showing where you need to aim to drift the bullet into the centre.

[native hunter]

Thanks snipe.!!
They definitely are worth a look.
Regards
Native

[curan]

Hi Native,

There is a whole lot of stuff posted at the following link:

viewtopic.php?f=4&t=9745

I chased rim thickness, overall weight and overall length on SK rifle match ammunition. Batch numbers were consistant in the comparisons.

The very brief summary is:
- Without running side by side tests, I am convinced that matching overall weight is worthwhile. My best shooting consistency comes from weight matching rounds in .01 gm increments.
- Rim thickness showed a difference in side by side tests, but not so much that I feel it worthwhile as an exercise for anything except benchrest. Fatter rims seem more consistant in my rifle than thin.
- Overall length never gave a big enough disparity to conclude anything.

I used a .223 cartridge for gauging for a while, and then spun up a brass holder that I can clamp to a vernier arm. It's a tiny bit quicker if you are doing heaps. They can be bought from hornady for about $80us, I believe.

These days, I weight batch, then gauge the rim thickness for the 3.34gm stuff (as there is lots of it in a brick), and keep a box worth of the thicker rimmed rounds for the bench. The gear between 3.33 and 3.35 (inclusive) I use for 3P and field rifle, and 3.32, 3.36 or 3.37 for silhouette. The rest is for practice.

I also got 4 lots of the "price sticker" style labels from the local office supplier in green (bench), yellow (3p or FR), orange (silho) and red (practice). This makes selection easy in my ammo locker.

What works for me may not work for you (obviously), but it may give you ideas on the direction you are heading into.

regards, curan.