I shoot 30br and last winter I made some changes to my shooting style and ended up shooting 5 5 shot groups in a row that averaged in the mid to low .1s. I was very pleased and load up 35 more 34.5gr H4198 rounds for a upcoming spring group match. After the match I had around a .320 average group size. The day was beautiful with little wind and what was there was moving directly downrange. I shoot with flags and probes. To say the least I was really surprised when the bullet God handed me this outcome. My question, after trying to figure what happened, how much affect does a 40 deg change in temperature affect H4198. I read that it was a load and forget type thing or did I misunderstand? If it is a factor what are some good rules of thumb? Thanks
30BR, H4198 and Temperature Change
- Thread starter Olde Man
- Start date
Did you shoot the agg in the low 1's in a match? Most everyone shoots better in practice.
Gene Beggs offered this general guide derived from countless visits to his own shooting tunnel: For each 10 degree F change , there is a 30 fps velocity change, i.e. T^/ go down in powder charge, and vice-versa. Despite what some read into Hodgdon's "Extreme" temp. stable powder, you will not maintain velocity throughout temp. changes. Some powders have other quirky traits, like Vhitavouri N-133, which acts goofy in low humidity.
Also, beware of days with "little wind" ....it usually brings slow moving mirage which is very hard to read. Lastly, if your wind moving downrange meant a tailwind, shooting your group with any small change in angle from a true wind out of 6:00 - say 5:00 < > 6:00 or 6:00 < >7:00 will result in a bigger group. If you shoot one at 5:00 and one at 7:00 then your group size may double.
Gene Beggs offered this general guide derived from countless visits to his own shooting tunnel: For each 10 degree F change , there is a 30 fps velocity change, i.e. T^/ go down in powder charge, and vice-versa. Despite what some read into Hodgdon's "Extreme" temp. stable powder, you will not maintain velocity throughout temp. changes. Some powders have other quirky traits, like Vhitavouri N-133, which acts goofy in low humidity.
Also, beware of days with "little wind" ....it usually brings slow moving mirage which is very hard to read. Lastly, if your wind moving downrange meant a tailwind, shooting your group with any small change in angle from a true wind out of 6:00 - say 5:00 < > 6:00 or 6:00 < >7:00 will result in a bigger group. If you shoot one at 5:00 and one at 7:00 then your group size may double.
When I was competing with the 30BR, my go-to load was always 34.2 grs H4198 with a BIB 118 10-ogive about .012 into the lands. Used Fed 205M & Wolf srm primers interchangeably with this load. It always agged well. I think LHSmith is probably right with his interpretation of your results. I would practice some more with the load you are using & simulate match conditions as well as you can. I think you will find that you shoot your best with winds from 2 to 4 or 7 to 10, and you will have the most trouble in head & tail winds. Let us know what you find.
A tuner will tell whether it's you or the load going away. It'll fix the load going out of tune but it won't help you read the flags.
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.