C.O.L. and your rifle chamber


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Lennyjoe
January 19, 2005, 11:58 PM
Ok, so I was reading an article in the new Shotgun news and tried it out.

The author had an interesting way of checking the chamber length in rifles. You take an expended brass shot out of your rifle, roll the case opening just enough to retain the bullet. Use a marker to color the bullet from base midway up and insert the bullet slightly into the brass.

Next you slowly insert the round into your rifle and close the bolt until it locks. The bullet will basically engage the rifling in the barrel and then push back into the brass. Remove the cartridge and then measure the C.O.L. for your rifle. You can also see how far to seat the bullet cause the brass will scrape off the ink as it enters the casing.

The author then goes on explaining the closer you have the bullet to the rifling the better accuracy. The bullet will have less turbulence due to no gap before the bullet exits the cartridge and engages the rifling .

I know there are guages out there to check this but I thought it was interesting and tried it out.

My reloading manual calls for a C.O.L. of 3.250 when in fact my rifle is measuring at 3.275

Am I in too deep here fellas or am I on a learning curve?

Or maybe I should order a Stoney Point for my calipers and be done with it.

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redneck2
January 20, 2005, 06:15 AM
check out Varmint Al's website

444
January 20, 2005, 08:14 AM
Warning: I am no expert on this subject, but I would love to see a conversation about this started instead of reading more about everyone's favorite 9mm.

The method you describe is better than nothing, however it is pretty crude. One problem is that bullets are not all the same length. Even bullets of the same brand, and type out of the same box. So, when you measure the OAL from the base of the case to the tip of the bullet, your results will only be in the ball park. You need to have a way to measure to the bullet's ogive instead of the tip.

Seating the bullet as close as possible to the lands is not nessessarily going to be the most accurate, although it might be. You usually need to do a little experimentation to find the distance from the lands that your rifle shoots best. This is usually the last step in developing the perfect handload. l

Swamprabbit
January 20, 2005, 08:51 AM
With some bullets, seating them to within about .015 of the lands gives you optimal accuracy. To do this right, you need to invest in the gauges - otherwise, you could have REAL problems. The biggest problem with the method you described is that when you close the bolt on the cartridge, there is a good chance that the bullet will want to stick in the rifling when you try to extract the round. Even if the bullet does come out in the case, it may have pulled back out some thus giving you a measurement that is actually longer than what it should be. The gauges work by a rod going through the bottom of a modifed case that pushes the bullet into the lands. Once pushed in, you can lock the rod in place with a tension screw. After the round is extracted, even if the bullet did stick in the rifling (easily removed by gently pushing a cleaning rod down the bore), the bullet can be seated back into the modified case back to where the rod is locked in. Now you can measure the OAL accurately.

Lennyjoe
January 20, 2005, 08:58 AM
I did some searching and found the Stoney Point guages that I will need.

Even if the bullet does come out in the case, it may have pulled back out some
Im assuming thats the purpose of the ink on the bullet. To see if the bullet actually pulled out a bit when the round was ejected.

It is in fact a crude way of doing it but was interesting to try anyway. The plan is to get the appropriate guages and properly measure my chamber for increased accuracy.

Valkman
January 20, 2005, 04:06 PM
In my very-limited-experience, the bullet sticks in the lands more often than not. I've used the Stoney Point gauge on my AR and I stick a cleaning rod or similar down the barrel or the bullet would stay. In the measurements I got, the ideal OL was longer than I could fit in the mag. I'll have to try it with my new AR and see if that's the case with it also.

Coltdriver
January 20, 2005, 04:56 PM
What you are doing is just fine to determine the OAL to the lands with the bullet you are using. Depending on the ogive of the bullet you use you may get different results.

I used the same technique and got accurate results on a per bullet type basis. Then I got the stony point tool. Its a little more precise.

So you can also see that your cartridge OAL minus the measured length to the lands gives you .015 jump.

If you stick with (no more than) the max OAL called out in your reloading manual you should be ok, assuming you have a standard chambering.

You will have to be a very good shooter to notice a difference in anything closer, however, that is the lure of hand loading. I would not go over the book OAL until you have a more accurate method of determining your dimensions. The pressure goes up dramatically when you get too close or if you touch the lands. You can blow up the rifle.

Conversely, Weatherby uses extra jump to increase the velocity of the bullet. I have a .223 that is shot out (throat eroded) enough that I can not get the bullet close to the lands and keep the bullet securely in the case. It still shoots very accurately for me. I can routinely hit a four square inch target at 200 yards with a 4x scope with this rifle. Good enough for varmints. I never tried it at a proper target range.

I am only one year into reloading, but the most important tool that I did not add early enough on was the stoney point tool. If you are working with a heavier caliber I would consider the knowledge of your actual chamber dimensions to be absolutely critical to your safety.

For the fellow with the AR the 5.56 chamber is purposefully longer than a sammi spec .223 chamber, hence you will not be able to get close to the lands and still fit in the mag. If you check the barrel on your AR I bet it has 5.56 stamped on it.

Valkman
January 20, 2005, 05:26 PM
For the fellow with the AR the 5.56 chamber is purposefully longer than a sammi spec .223 chamber, hence you will not be able to get close to the lands and still fit in the mag. If you check the barrel on your AR I bet it has 5.56 stamped on it.

Bingo! My new Colt 6721 will probably measure the same way then since it's 5.56 also.

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