30BR Load VS Air Temperature Info

[Olde Man]

I am new to the BR sport and an shooting a 30br, Cheeks 115, 34.5 gr H4198, .010 into the lands with a velocity of 3050fps. I developed this when the temp was 45 Deg and it is not working in 85 Deg temps. If you can get me close I will fine tune it. The other question I have is how long can I leave a round in the chamber with the bolt closed before it starts to make a difference on my 2nd, 3rd, 4th or last shot. My starting groups are in the 1's and 2's and then I open up to .400 or better as I wait for the wind conditions to look better later in the day as it warms up. I know this seems obvious but I was looking at everything except the basics. Thanks

 

[artbosco]

The other question I have is ... how long can I leave a round in the chamber with the bolt closed before it starts to make a difference on my 2nd, 3rd, 4th or last shot.

I copied this from benchrest.com into my Benchrest file quite a few years ago. I often use it as a reminder. You might read it for what it's worth.

"Don't let rounds sit too long in a hot chamber" ... by Jackie Schmidt

Don't let rounds sit in the hot sun.

Don't let rounds cook in a hot chamber for more than 45 seconds.

Dump the round on the sighter and start over.

Many of us have tested this for ourselves. About two years ago, I spent the better part of a good hot day, shooting groups over my 35P Chronograph to see for myself how letting a barrel sit for minutes between rounds, and letting rounds sit too long in the chamber, affected the Rifle's agging capability.

Using my Rail Gun to keep as much of "me" out of the results as possible. I came away with the conclusion that what I had been told was true.

***Do not let rounds "cook" in a hot chamber, do not let rounds sit in the hot sun, and if you have to wait on a condition for more than 40 to 50 seconds, dump the chambered round on the sighter and start over.***

The strange phenomena is that sometimes the cooked rounds would go in, sometimes not. The percentage of "cooked" rounds not going into the group was about 80 percent greater than any others, especially when shooting 10 shot groups.

At The Bluebonnet this year, I made the mistake Sunday afternoon of letting a round sit in the Rifle for a long time. I had three shots in the group, and I was shooting a specific condition, in other words, no hold. For some reason, I went "stupid", and forgot about how long I had let that round cook. In my excitement of seeing the condition coming back, I let it go, and it went high and against the condition, a good bullet holes worth. The fifth shot, which I waited again on again but without letting the round sit in the chamber, went into the original three.

I know that is strictly anecdotal, but that very same thing has happened to shooters many times.

Experience Benchrest Shooters will not let a round sit in a hot chamber, or wait too long between shots without putting a round on the sighter to keep the barrels tuning characteristics consistent.

 

[searcher]

I would try backing off the powder 4/10th of a grain and shoot over your chrono to see how close it gets to your cold weather load velocity - then adjust as necessary.

As for leaving a loaded round in the chamber while waiting for conditions to improve - when I am shooting in conditions that do not assure me I will be able to shoot the next shot as soon as I am able to acquire a good sight picture, I don't load until I feel the condition has changed to my favor. If I get caught in a change with one in the chamber - I'll usually remove it and place a cool one in the action if it had been in there more than 20 seconds or so - but not close the bolt until the condition improves. The big variable is also how many rounds you have fired. f I had only fired two rounds - I might be inclined to let it go a bit. If I just smoked off 6 or 7, I'd pull it out. Bottom line - you want it in there for NO longer than need be.

 

[artbosco]

Are you shooting over a good set of wind flags? Are you looking for a predominate condition to shoot in? If not, you need to do both.

Work up a new load starting from scratch. It won't take long. You might start at 33.8 and work up in .2 increments to maybe 34.6. 15 rounds each. 3 five-shot groups each. When you find what your barrel seems to like, shoot .1 grain on either side. Then start at just touching the lands [a thin circle around the bullet] and work inward. Try bushings .001", .002" and .003" tighter than your loaded round's OD at the pressure ring.

What's your chamber size? What do you turn to? For example mine is .330" so I turn until I achieve a .328" OD [with a Cheek 118 9 Ogive bullet seated in the case].

Most everything you need to know about the 30BR is right here: http://www.accurateshooter.com/cartridge-guides/30br/ Click the highlighted and underlined words for additional info.

If you're very new, attend some matches and ask a bunch of questions.

 

[GSPV]

See below

I'll add to that that most people that I know now say that 1.5 thou per side is the starting clearance. Also, 2-3 thou bump rather than 1-1.5 that is familiar to the PPC guys.


Al Nyhus
Registered User
Join Date
Feb 2003
Location
Lower Dakota Territory
Posts
1,394
Johnny, my 'baseline' for working with my 30BR stuff is H4198, a bunch of neck tension (.004 under what a loaded round measures), a good amount of jam (.025-.030 from 'just touching'), Fed 205M and either a BIB 118-7 or lately my own 117's. My barrels are all twisted 1:17. As for neck clearance, .002 is a good place to start..but one of my Kostyshyn barrels just really came alive after I opened the neck clearance to .004. I don't recommend doing this from the start, but it does show just how individual some barrels are. Seating depth falls into this same area.

When it comes to bullets, my belief is that bullets is one area that more 30BR shooters should experiment in. Even though all of the commonly available BR .30 cal. bullets are great (BIB, Cheek, Euber, 10X, etc.), some barrels simply like a particular bullet more than others.

I have several brands of .30 cal. bullets here, as well as the ones I make, and use them during testing to see whether a certain combination shows the same 'trends' during tuning.

Good shootin'. -Al