Who shoots heavies in their 308?

[GJgo]

First range test

Made it to the range yesterday with my first loads for the rifle, 200gr Matchkings in front of Reloder 17. Unfortunately I didn't have my Chronograph with me so I'll have to bring it next time. At first I noted that my POI was pretty darn consistent across the charge range. Then upon closer inspection it actually looks to be decreasing a bit with hotter charges, which seems odd.

You can see it start out close to one accuracy node, then open up in the middle loads, then shrink back down towards another node. It's pretty neat to watch this happen.

The holes on the bottom were me finding my POI. Had to come up about 3 clicks & left a few clicks compared to the Federal GMM 175 SMK POI.

I was fireforming new Win brass so I didn't want to eat up my stash of BR2 primers, so I just used standard 200s. Brass prep & better primers should help later on. This first test was really just to get in the ballpark.

Looking good so far. The powder is pretty compressed at the upper end, but still no pressure signs. Seems typical of what I've read on the 308 & RL17. Next I'm going to alter the seating depth and try up to 48gr. I know guys have run up to 50 with the 208 Amax, but that's in rifles with longer throats. They tend to settle in the 48-49 range from what I've read. They all say that the velocities skip up in small increments to a point, then there's a noticible step up point- I'll be keeping an eye out for this with the chrony & watching the brass.

If I can get 1K capable velocity with these 200s & find a load in the half inch range I think I'll call it good. If the speed isn't there I'll try some 190 SMKs.

Thinking about skipping the VLD testing for now because the RCBS comp seating die I have is giving me about .005" bullet runout on a case with .001" neck runout. I think the SMKs will handle runout better tha a VLD will, unless I jam to straighten it back out. Hmm..

 

[Greg Culpepper]

For the flattest trajectory and least wind drift, you need to work out which bullet has the shortest time of flight out to your intended range.

Alpacca,

It is perfectly correct that flatest trajectory and time of flight are related but it is commonly held, intuative and wrong that time of flight has anything to do with wind drift. The only thing that determines wind drift is time lag which is consequense of drag/bc.

There are three long discussions of this fact on this board. Search for "Attention all ballisticians" and "For you ballisticians". The first of those long threads was something like What exactly does the wind do to a bullet. Major contributors included Gene Beggs, bench rest inventor of renoun and possibly the greatest aerobatic flight instructor in USA history and Bryan Litz, Berger Bullets' ballistician, ballistics author, software developer and an honest to gosh rocket scientist to boot.

Greg

 

[alpacca45]

Alpacca,

It is perfectly correct that flatest trajectory and time of flight are related but it is commonly held, intuative and wrong that time of flight has anything to do with wind drift. The only thing that determines wind drift is time lag which is consequence of drag/bc.

There are three long discussions of this fact on this board. Search for "Attention all ballisticians" and "For you ballisticians". The first of those long threads was something like What exactly does the wind do to a bullet. Major contributors included Gene Beggs, bench rest inventor of renoun and possibly the greatest aerobatic flight instructor in USA history and Bryan Litz, Berger Bullets' ballistician, ballistics author, software developer and an honest to gosh rocket scientist to boot.

Greg

Thanks Greg,

I checked the threads, and, you know what's very embarrassing?

I started to remember getting my head around the idea of wind drift being proportional to change in velocety, back when I first read Geoffrey Kolbe's ballistics hand book http://www.amazon.co.uk/Ballistics-Handbook-Geoffrey-Kolbe/dp/0953753700/ref=sr_1_1?ie=UTF8&s=books&qid=1269279719&sr=8-1

All the more disgusting that I not only returned to a state of darkness, but spread it about a bit too

 

[alpacca45]

One of the other things I remembered reading (I think it was in Kolbe's book too) was subsonic .22 lr rf having less wind drift than std velocety .22lr.

Which is certainly another way of saying, the faster you launch the same bullet, the faster its rate of decelleration.

Perhaps I need to start reading up on the "whisper" loads

 

[Greg Culpepper]

Alpaca,

Happy to help. Now would you return the favor and teach me how to spell consequence? Sheesh. I wonder if I correct my post if it will fall through to your quote of me? Oh well. Plenty of embarrasment to go around.

Greg

 

[GJgo]

Went back to the range today with the chronograph, worked up to 48 grains. It was pretty compressed up there. 47 shot the same as last week, and 47.5 shot the same as that. At 48 grains however I dropped 4 shots into .250" which got me excited. The chrony reported 2635 fps at 48gr. No pressure signs on the brass, none on the bolt lift, and the calipers measure the cases to be the same as all the colder loads. Not sure if I can fit any more powder in there at this OAL, I'll have to work up some back up loads to check for consistency.