flat base vs. boat tail

[akajiggs]

Been doing some shooting my old 6mm lately.It is an 80 model Remington Varmint Special.5 days ago I shot some pretty good groups with this thing.2 groups with one load group measured .219 and another measured .235 c-c. I thought this was pretty good for a factory rifle that has not had anything but wooden stock bedded.
Had 75 gr. SI HP's flat base bullets loaded same as the other day and went back to range yesterday.This time I started at 200 instead of 100.Groups went to about 1.5".No wind,very good day.Went to 300 and it opened up to 2.5".
Needless to say,I was very disappointed.I then went back to 100 and shot a group about .25.
Could the problem be the flat base bullets just not flying well at longer distances and only at short distances?Would the boat tail fly better at a longer range?
Your thoughts would be appreciated.
Jim

 

[potatoe]

That's not bad for a factory rifle, its sub MOA. Are you in the middle of your node? What did the groups look like. Flat bases might get a little more deflection but I would shoot them out to 300 all the time if that's what the gun liked.

 

[LHSmith]

Wind and mirage. Until you put some form of wind indicators out between you and the target....you really have no idea what is happening out there. Your problem is not with the FB bullets if they are regularly grouping at 100 yds. as you say. What is the average group size shot @ 100? One or two small groups are nice, but what matters is what the gun/load can be expected to perform at consistently. Lastly,are you certain you have adjusted the scope for parallax at each tested range?

 

['Freak]

Thinkin’ boat tails eventually do fly ‘better’ than otherwise similar flat base projectiles but eventually don’t kick in until beyond a couple or three hundred yards.

 

[akajiggs]

yes sir ,parallax was adjusted at each range and focus and no mirage.I thought about the wind maybe causing the problem but thought the groups would be pushed to one side or the other.but at longer ranges,1 shot would be low,next would be high,next would be right and so on.
With this particular load,I have shot a lot of groups. All groups will average .221-.3".Every once in a while,I will throw a shot but can always call them.
I know this is a hunting rifle and not a bench rifle but really expected it to do better at 2-300 yds.
Thanks again and appreciate all the help
Jim

 

[LHSmith]

^^^^^ Did you adjust to get parallax free, or did you just turn the adjustment to the numbers inscribed on the scope? FWIW parallax and focus are not necessarily in concert with one another in all scopes.

 

[LHSmith]

^^^^^ My best guess is mirage effects. What kind of scope? Time of day? Sunny, overcast, mix? Type of terrain, bare ground, grass? Ground moisture, recent rain?

 

[Richard Jones]

.........Until you put some form of wind indicators out between you and the target....you really have no idea what is happening out there........

 

[sbhooper]

I would say that your rifle just does not like the fb bullets as well as it likes the bts. Barrels can be finicky. Usually, it seems to me that it is the fbs that shoot better, but my 6mm rem shoots them interchangeably.

 

[Shynloco]

oldwildhog,
You've touched on a topic that I've found both interesting and important to my accuracy. I shoot strictly 100 yds (Benchrest), though I've tested my theory shooting longer distances in the past. I tested this flat base/bt effect and have found that in three out of 4 calibers (6br, 6.5BR, 30BR and .308) I reload for, the BT's are better in performance than are the BT's AT 100 YDS. In the one (.308), I had to shoot BT's because of the bullet (168gr HPBT) I use that isn't made in FB. I found my 5 shot groups are actually tighter than what the BT's provide at 100 yds. And I'm talking all Match Grade barrels. I also noted that the further out I went, that there was a dropoff in performance and thus group size using FB's. Now based upon what I've experienced, read and been told by some competitors I know, the advantage shifts to BT's once you get to 400+ yds and certainly at 600 yds - 1K for aero reasons which makes perfect sense. Just my .02 worth.

Alex

 

[Tim Singleton]

Wind and mirage. Until you put some form of wind indicators out between you and the target....you really have no idea what is happening out there.

Very true. And even with flags a very light changes are hard to see that have a major effect at 200 and 300 yards

The target below is what happens on a dead calm morning and you miss a small push in the wind that hardly wiggled a flag tail

 

[potatoe]

^ Son of b!#$. was that shot 5?

 

[Tim Singleton]

Yeah. I about cried

 

[Shynloco]

There is no doubt in my mind that what LH and Tim write is absolutely true and adds yet another layer of "concern" to this discussion. I consider wind and mirage just another "challenge" (or variable) when shooting or even testing. Even duplicating all those different considerations LH wrote about, is very difficult and nearly impossible day to day. That's perhaps why I believe, shorter distance shooting removes or lessens some of those concerns and allows for a cleaner test in a particular rifle in such a comparison of bullets (fb vs bt).

Alex

PS. Nice shooting Tim. Probably just God's way in making us all humble.

 

[LHSmith]

yes sir ,parallax was adjusted at each range and focus and no mirage.I thought about the wind maybe causing the problem but thought the groups would be pushed to one side or the other.but at longer ranges,1 shot would be low,next would be high,next would be right and so on.

With a 12x scope, it will be hard to pick up mirage. On a typical match day when conditions would be considered "benign" by non-competitive shooters, the windflags (dozens of them) often will show a left to right push in the front sets of flags, and a right to left push in the back field flags. Add in cloud/sun mix at intervals, and flags may be going multiple directions and speeds. Add in different terrain at the various match venues each of which has it's own effects on the wind and you can understand why some find BR so challanging.
Generally, wind will cause horizontal with slight elevation dispersion. A large amount of vertical is a sign mirage was in play, especially if conditions appeared to be "calm."
Let us know if this helps.

 

[jbarnwell]

Tim, your target is a good example of why most benchrest shooters have gray hair!

 

[Tim Singleton]

Tim, your target is a good example of why most benchrest shooters have gray hair!

I heard that.

A lot of guys just can't accept how much the wind will move a bullet as close a range as 200. Very slight changes that are hard to see with 8 flags placed have a big effect. Shooting at 200-300 yards with the purpose of testing a load or bullet without flags. IMO is pointless

 

[akajiggs]

When I adjust for parallax,I adjust where everything is sharp and clear .I don't go by numbers. Now i did have a lot of ground moisture that day and was a lot of moisture in the air,but we always have high humidity here in Arkansas.It was solid cloudy and 60 degrees that day or morning. Mirage was none.Good sharp clear target .
I am not going to give up.Reloading for next week as we speak.
I will be trying some BT's though just for the sake of trying.
Remember,this is just my crow gun.
Thanks again
Jim

 

[LHSmith]

Again, you won't see mirage unless you have > 20x optics. Also, it isn't the FB bullets. IMO you won't do better accuracy wise than your load with FB bullets...groups that size are exceptional for a factory gun. Don't change anything until you nail down the problem, or you'll be forever chasing your tail. The fact that you had a lot of ground moisture is key and could have presented slow moving mirage which is hard to pick up versus the sun induced mirage most are familiar with.
On the parallax, check for it by moving your eye side to side/ up and down.....it is free of parallax when the reticle does not move one iota.

 

[snert]

Moisture, 60 degrees, sun and a 12X= mirage/ 3 inch groups. Your gun is shooting great. Keep shooting it. You will likely find it improves the more you shoot it.

Snert