Pressure Spike Anomalies

[DrThunder88]

For my .243 Winchester I've been running 115gr Berger VLD hunting bullets with 46.0 grains of H1000 in Hornady cases and a CCI BR-2 primer. I have been getting very consistent chronograph readings of 2890 fps all summer. We've had a couple cool days, so I decided to get some 60 degree F data to go along with my 70-80 degree data. I brought with me ten rounds of the batch I took to Bang Steel, the only difference being these were in brand new cases, five of a more recent batch in once-fired cases, and five in once-fired cases with bullets I'd pulled from other loads. For brevity's sake, I'll call them Loads 1, 2, and 3 respectively.

Straight out of the case the rifle put a round of Load 1 right in the center of the bullseye at 100 yards, which was not bad for having not cleaned it since my last range trip. I attached my MagnetoSpeed to the barrel and took another shot: 2916fps. "That's a little hot for cool ammo," I thought. The shot landed just beside the first shot, despite my awkward, semi-prone shooting position. Four subsequent shots showed pretty good ES of 9, but the average was 2911 fps. Load 2 was slightly hotter at 2919 with a 14 fps ES. When I finally shot Load 3, I found much more familiar numbers: 2894 fps and ES of 36 (2885 and 23 fps excluding one 2900+ outlier).

My load is 1% over the published max Lee has for 117gr bulets, but the velocities have seemed in line with a lighter projectile and longer barrel. Still, I'm wondering why a cooler round on a cooler day could be having such high velocity readings. I tried (somewhat unsuccessfully, I might add, chilling a baggie of rounds in a bucket of ice water for varying lengths of time before shooting to get velocity data only to find there was no appreciable difference between 60 and 80 degree F ammo and only a 20 fps difference between that and 40 degree F ammo, though that was not too far from my ES from either temperature.

I should also say I didn't fire them all in a string, one load after the other. I tried going round-robin with a few generous cool downs for the barrel. I also noticed the MagnetoSpeed had slid forward slightly, though it seems like that would make the velocities measure as slower rather than faster.

[yobuck]

It might just be a what you dont know wont bother you situation.
Id personaly be happy if the gun shot well.
But admittedly my mind works differently than some others.
To me a pressure spike is when i have to stand up to open the bolt. lol

[LoneWolf]

Some of these powders are very stable. I've had good luck with both H100V and H4350 in my 243 setups. I started with the 115 DTACS, then moved to the 105Berger Hybrids, I'm going to try to tune it in next weekend with the 105AMAXS and H4350.

With 41.5hrs (work up to this if tried) I get 2965fps and if firing a fast string I've had it get up to 3000fps as the barrel warmed. If fired normal and slow I had an ES of 10. I believe barrel temp and elevation has more affect on velocity than ammo temp.

I've been to matches in the mountains that I had to knock .2 mils off of all my dope or I was shooting over the top of all the targets.

I'd say everything is running smoothly for you.

[darkker]

Remember the 243 is one of those infamous cartridges with a known habit of Pressure excursions, with no rhyme or reason.

[LongRange]

group 1 is most likely case capacity because they where new cases which equals less capacity...as for 2 and 3...could be a lot of different things...if you really want to figure it out id start by seating a bullet in a case and pull it taking note of the force it took...then pull a bullet from a loaded round you've had sitting around and note the force to pull it...id then take the cases from the 3 groups and a few new cases(if you still have them separated and if you have a few new cases)and weigh the cases dry and write down the numbers then weigh them with H2o and write the numbers down...personally id weigh every case with H2o since its hornady brass.

[DrThunder88]

I'd not heard of the .243 Winchester's reputed propensity for pressure spikes. Very interesting, thanks! Still, it looks like the situation wasn't as bad as I thought in terms of downrange performance. I had somehow gotten a 0.5 mil difference in elevation at 100 yards corresponding to the difference in velocities. When I ran the numbers again and double checked them, the actual elevation difference is closer to 0.1 mil, which is undoubtedly better than I can hold at 1000 yards.

Speaking of elevation changes, I forgot to mention I noticed a POI shift of about 0.5 mil down shortly after the first few shots, which I attributed to very bad bipod technique and a very awkward position.

[LoneWolf]

I'd not heard of the .243 Winchester's reputed propensity for pressure spikes. Very interesting, thanks! Still, it looks like the situation wasn't as bad as I thought in terms of downrange performance. I had somehow gotten a 0.5 mil difference in elevation at 100 yards corresponding to the difference in velocities. When I ran the numbers again and double checked them, the actual elevation difference is closer to 0.1 mil, which is undoubtedly better than I can hold at 1000 yards.

Speaking of elevation changes, I forgot to mention I noticed a POI shift of about 0.5 mil down shortly after the first few shots, which I attributed to very bad bipod technique and a very awkward position.
Sometimes with low recoil setups we forget how important recoil control is! I caught myself a few times after I went back to the small plate at 851yds where I had a miss I could not attribute to incorrect data and put 7 out of 10 on it last weekend after the match was over.

This is why I'm going away from the Harris Bipod, for the ATLAS, but then I thought I was never really satisfied with the ATLAS either, so I ordered an Accu-Tac SR5. Should receive it mid week and run it on Friday.

[yobuck]

Everybody should visit a 1000 yd (benchrest) match and spend time talking to the shooters and evaluating the results.
Be aware that many of these people also hunt long range, and some even shoot in other type matches.
See if they would rather shoot prone/bipod or from a bench for accuracy given the choice.
The best loads possible are still but one part of the total picture.

[eddiesindian]

It might just be a what you dont know wont bother you situation.
Id personaly be happy if the gun shot well.
But admittedly my mind works differently than some others.
To me a pressure spike is when i have to stand up to open the bolt. lol
agree......completely
Its so dam easy to over think things. Ive been reloading for the past 35yrs and if its one thing Ive learned is just that. Id say that's what makes this sport so interesting.
I guess everyone of us reloaders/shooters goes thru there own process.
Id have to say that if it shoots well and you've completed your load development then have at it. Go out shoot it, work on other factors such that of reading winds and mirage, baro pressure,temps. 1st rd hits at 1K (IMHO) seem to be more gratifying. Unless of course you don't have the area to send them that far.

[LongRange]

I can vary my FPS by 25 to 30FPS by loading or not loading the bipod...I also stay on target if I load the bipod and loose sight if not loaded...so while ppl always talk about over thinking theres something else for you to think about...its all about consistency...from seating the primers all the way to pulling the trigger and anyone that says different don't shoot consistently at longer ranges....this is not meant as a smart a$$ remark or aimed at anyone its just a fact.

[yobuck]

I can vary my FPS by 25 to 30FPS by loading or not loading the bipod...I also stay on target if I load the bipod and loose sight if not loaded...so while ppl always talk about over thinking theres something else for you to think about...its all about consistency...from seating the primers all the way to pulling the trigger and anyone that says different don't shoot consistently at longer ranges....this is not meant as a smart a$$ remark or aimed at anyone its just a fact.

Well loading a bipod by which i assume you mean foward pressure, might help staying on target. Ive heard others say leaving one leg notch exposed helps keep the jump down, especially from a bench. But im scratching my head over why differences in velocity by not loading the bipod legs.
Now yanking the trigger really hard might be something i could relate to. Maybe even pressing the tounge real hard against the roof of your mouth while really yanking the trigger. lol

[LongRange]

Well loading a bipod by which i assume you mean foward pressure, might help staying on target. Ive heard others say leaving one leg notch exposed helps keep the jump down, especially from a bench. But im scratching my head over why differences in velocity by not loading the bipod legs.
Now yanking the trigger really hard might be something i could relate to. Maybe even pressing the tounge real hard against the roof of your mouth while really yanking the trigger. lol


Come on buck your slipping....its the difference in recoil....no load equals free recoil which reduces velocity.

[sharpshooter]

Come on buck your slipping....its the difference in recoil....no load equals free recoil which reduces velocity.

That sounds plausible, but I'm not buying the 25-30 fps. You need to run that experiment again, only this time from a rest, not a bipod.

[LongRange]

That sounds plausible, but I'm not buying the 25-30 fps. You need to run that experiment again, only this time from a rest, not a bipod.

The load im shooting now in my 260 shoots a consistent 2810-2825 when i load the bipod...with no load on the bipod resting on a rear bag its 2795 to 2805...next time i go to the range ill try it off a bench with bags.

[darkker]

DrThunder,

The 243 & the 7mm RM have a very long well known history of Pressure excursions. The 7mm problems are expounded upon thoroughly in the A-Squared manual. The 243 may or may not be mentioned there, but every powder valuation I've talked with is well versed with it.