.17 hmr accuracy

[The Duncan 802]

Hi folks. This isn't a willy-waving 'how bleedin accurate am I' thread before anyone starts , more looking to swap notes.

On tuesday I fitted and zero'd a new scope to my hmr and was generally very pleased, especially as the extra magnification allowed me to print some really tight groups out to 150 yards.

I noticed though as I started to plough through some rounds, that the groups started to open up quite alarmingly! The 150 yard group went from 5p coin size for 3 shots to 4 inches!

At first I suspected barrel fouling (by that point I'd got through 60 or 70 rounds), but then I touched the barrel - pretty damn warm!

I cleaned the rifle that evening and took it out again today for some practise - all bang on again from the first shot to the last This time I gave the gun chance to cool for a minute after 3 or 4 shots and the groups remained very tight.

 

On the point of cleanliness - one of my friends had an Anschutz hmr and said it would only be spot on for a few shots before needing a clean again. But with my Weihrauch I am blessed with spot on accuracy for a box or more of bullets at a time - is that down to differences in rifling?

And how long do others find their rifles are accurate for, between cleaning sessions?

 

Cheers all

 

Duncan

[tegater 789]

Mine remains accurate enough for what I need but I clean religiously after every 20 or so shots at the moment. What you are seeing firing so many shots over a short space of time is Definatley a change in the harmonics of the barrel as a result of it heating up.

 

This is the one main reason why any person who has to rely on a first round kill will always zero on a cold bore. ( it can be a time consuming process)

 

Sounds like you have had some good group though!

[richmcgin 32]

Normally i will always check zero after a clean with one fouling round before i start, but i dont clean then as much as some people. i hate the job, last cleaned my 17 about 3 years ago but in all honesty its only had one or two shots though it in that time, my 22 gets a clean after about 100 rounds and the 223 about every 20. the 223 heats up quick so i try and use 2 shots to zero but it can be a pain when testing new loads, after 10/12 shots the groups start to open out so i like to test with 3 shot groups when possible.

[The Duncan 802]

Mine remains accurate enough for what I need but I clean religiously after every 20 or so shots at the moment. What you are seeing firing so many shots over a short space of time is Definatley a change in the harmonics of the barrel as a result of it heating up.

 

This is the one main reason why any person who has to rely on a first round kill will always zero on a cold bore. ( it can be a time consuming process)

 

Sounds like you have had some good group though!

 

In normal circumstances I'm about the same, every 20-30 shots I clean it pretty thoroughly and don't find it a massive chore. That said, I've had 60-shot practise sessions conducted at a more leisurely rate and the groups didnt open up at all which certainly showed that rate of fire has an impact on accuracy. Bore fouling after 60 shots certainly wasn't an issue.

Harmonics? Or heat expansion? I assumed that the warmer barrel expanded enough to make the bullet a looser fit, compared to how close the fit is between bullet and barrel when the barrel is cold, which led to wider groupings.

 

 

Thanks! I was very pleased with the results to say the least. The Weihrauch is an easy rifle to shoot and flatters whatever meagre skills the shooter has . I was in the zone today too, focussing on the details and actually being strict on technique. It was a good distraction too given a personal events recently.

 

cheers

D

[zx10mike 137]

my anschutz groups 2" at 100 with winchester and 1" with hornady.5p groups is amazing with rimfire.my 204 will do that so i know its not my shooting.

[IanB 0]

My experience with HMR's, if your shooting any quantity of rounds, they just open up, unless cleaned very regular.

[tegater 789]

Mine remains accurate enough for what I need but I clean religiously after every 20 or so shots at the moment. What you are seeing firing so many shots over a short space of time is Definatley a change in the harmonics of the barrel as a result of it heating up.

 

This is the one main reason why any person who has to rely on a first round kill will always zero on a cold bore. ( it can be a time consuming process)

 

Sounds like you have had some good group though!

 

Harmonics? Or heat expansion? I assumed that the warmer barrel expanded enough to make the bullet a looser fit, compared to how close the fit is between bullet and barrel when the barrel is cold, which led to wider groupings.

 

 

D

The colder a barrel gets,the more the metal contracts, and the opposite occurs when the barrel gets hot. When the AI's were first used in arctic conditions, the extreme cold resulted in increased breach pressures which altered the harmonics and the fall of shot.

I stand to be corrected, but I believe that when the barrel gets hot, the barrel expands opening up the overall diameter. This is worsened in thin barrelled rifles and less so in varmint or heavy weigh barrels.

[The Duncan 802]

Looks like we're on the same wavelength Tegater

[tegater 789]

Yep, and looks like we are going to get some great hmr weather over the next few days!

[matt_hooks 188]

The expansion of diameter would vary depending on the barrel form. What I think is more relevant in terms of thermal expansion would be a lengthening of the barrel, which will inevitably change the barrel harmonics.

[will84 10]

What are you guys using for cleaning the barrel??

Will a bore snake do a good enough job??

[Extremetaz 15]

Looks like we're on the same wavelength Tegater

 

aah-haw-haw

 

don't worry - I saw what you did there.