Crazy, or am I???

[lefty315]

Has anyone ever seen this before? I have a .450 Marlin Guide Gun that I have been shooting for years. I normally load the Rem 405 grain just a touch over 1700 fps. It is on the verge of wanting to knock my teeth out when I pull the trigger off the bench but it is spooky accurate. I am not bragging but it constantly shoots clover leaf holes at 100 yards with a peep sight.

My grandpa had a bunch of 350 grain flat points he gave me so I thought I would try some milder plinking loads. I found some loads from a magazine using an actual guide gun and H4895. I started lower than his lowest load which should have put me several hundred fps below my 405's. Shot around 8 to 9 inches high?? As my powder charge increased the 350's started to impact lower on the target. Weird.

I have seen this before with hot loads in a handgun impacting lower than milder loads but never in a rifle.

 

[JD338]

lefty315,

Welcome back, its been a while.

As the barrel rises during recoil, the slower/heavier bullet leaves the barrel later than a faster moving bullet so the POI is higher.

JD338

 

[lefty315]

That much I get but shouldn't this bullet, which should be much slower than the 405, be hitting lower? I could see if these 350's were moving along pretty fast. When I shoot the 325 grain Lever Evolution rounds it impacts about 8 inches higher than my 405. And I am sure they are smoking along close to 2000 fps, if not faster. These 350's should be somewhere in the 1300 to 1500 range. 50 grains in weight to me does not seem like much when I am looking at an already big chunk of lead. Perhaps it afects it more than I thought it should.

 

[DrMike]

lefty315,

It is not an uncommon observation. JD338s explanation is a plausible explanation, and likely correct. It would appear that you didn't chronograph these loads, choosing rather to estimate what their velocity should be. However, bear in mind that you may be dealing with a difference in bearing surface and/or jacket material, which can spike pressure giving unexpected velocities. If the base or jacket material is sufficiently soft, obturation could easily account for the difference in velocity and the lowering of POI as deformation is more pronounced as pressure increases. Without actually inspecting your bullets and measuring, it is almost impossible to give a definitive answer to your question other than to say that, "Yes, this phenomenon has been observed in a surprising number of cartridges."

 

[Antelope_Sniper]

Lefty, it's a different load.
ANY change in a load can effect the point of impact. I've had points of impact change 12" with just a change in primers. 2 Bullets of significant different constructions could be 12" apart, nothing unusual there.

My buddies 300 RUM shoots the 150 and 180gr Sciracco's 2 feet apart at 100 yards.

 

[lefty315]

Thanks JD338, Dr Mike and Antelope Sniper(see, if you would have replied I would have added your name too :mrgreen: ) for the comments. I makes sense when you think about it but I have never experienced it before in such an extreme impact difference on the target. By the time I was done, with the hottest of my milder loads, the impact was about 2 inches high at 100 yards. I may go up in powder a little more to see if I can get it right on. It is still pretty mild compared to my jaw-breaking 405 loads but it will definately work.

 

[Guy Miner]

Hey Lefty - check the velocity of your loads. I saw some SIGNIFICANT changes in point of impact with the .45/70 and different bullet weights. Your .450 is very similar.

Regards, Guy

 

[lefty315]

Hopefully I can get out and check the velocity this week. School is about to start up again and my life will be altered having to juggle all the kids activities again!!!!

 

[filmjunkie4ever]

As these good men said different loads and bullets are a different ball game but in some of my rifles I have noticed a trend of heavier bullets shooting higher than lighter ones. For example if the gun is sighted in for heavy loads, it will shoot the lighter bullets to a lower poi. And vice versa with the gun being sighted in for light loads it will then shoot higher with heavier bullets. This is not an exact science as I have only noticed this as being the case in some rifles. Sometimes it will be a diagonal pattern or a horizontal pattern still, seldom do we see rifles which cast different loads to the same poa at 100 yards. Just my $0.02-

Dale

 

[SJB358]

lefty315,

Welcome back, its been a while.

As the barrel rises during recoil, the slower/heavier bullet leaves the barrel later than a faster moving bullet so the POI is higher.

JD338

Jim is right on. You notice it a bunch more with the slower movers than with the fast, light bullets. I will say that my Guide rifle shoots alot of bullet to the center of the target, just elevation differences depending on velocity. I wouldn't worry too much as long as you have enough adjustment. Don't worry about the Guide Rifle knocking teeth out, imagine what it does to animals!!! Scotty