How Does Twist Rate and Bullet Shape Affect Accuracy?

 

  

 

 Ballistics is a Black Art, well not really but it sometimes seems to be with so many variables involved that subtle changes to bullet weight, powder, primer, OAL, etc, etc can have dramatic results
Usually, with 9MM at minor power factor we find that great accuracy can be obtained with all weights and shapes from 115RN to 145RN/HP and, most competition shooters will have a preference for light, medium or heavy bullets that give a perceived difference in recoil – either slower/softer (heavier bullets) or snappy/quick (lighter bullets) for faster slide movement and perceived quicker follow-up shots). Now, how can you have the same perception (at identical power factor) you ask? - see what I mean about ballistics being a black art when we start talking about perceived differences). The difference really comes down to the preference of the shooter and sometimes their level of skill. Slower, heavier bullets will allow the shooter to more easily see the full recoil arc and therefore enable to “call the shot”. Lighter bullets tend to move the slide faster and can allow for a quicker follow up shot. However, if we get too caught up in the “feel” we are relegating accuracy to a secondary consideration. Without going in to how powder or other variables can affect accuracy, some individual pistols will be inherently more accurate with certain weights or shapes and this I believe is as important or an even more important factor in selecting the perfect load for your competition ammo. There’s more on the choosing heavy or light bullets at https://tigersharkballistics.com.au/pages/recoil-heavy-or-light-bullets

When we start getting into Major Power Factor for Open division pistols other things come in to play such as requiring loads that produce enough gas to work the compensator/popple holes to minimise muzzle movement in recoil. In Major PF barrel twist rate and its relation to bullet shape can become more of a factor affecting accuracy. Generally speaking, heavier (longer for calibre) bullets require a higher twist rate to optimise stability with pistol barrels being produced anywhere from a relatively slow 1:32 to a fast 1:10. Barstow Barrels are 1:16 with Schuemann offering 1:16 to 1:32. Some bullet shapes are inherently more stable and at Major PF velocities the difference in stability can be more noticeable and is evidenced in better accuracy. Tigershark “Hollow Points” are markedly different in shape to the equivalent weight round nose projectile with much more of a truncated cone shape compared to the tapering ogive of a round nose. It is thought that this shape is more inclined to stay on axis to target particularly at high velocity and may explain why many Open division pistols shoot very accurately with HP's.
Yes, it's a black art but once you find a load combination that works for you, stick with it.

 

 Accuracy testing in 38 Super using cast lead,
Tigershark 123 RN & HP's

Note that Tigershark bullets are factory rated to 1500FPS velocities higher than that can have a detrimental effect on accuracy as the bullet can become distorted and unstable. The minimum velocity in Open division for a 123GN bullet is just over 1300FPS so usually, this is not a problem.  

Testing credit to T Mason.

More information on twist rates at  http://www.schuemann.com/Portals/0/Documentation/Webfile_Barrel_Twist_Rate.pdf

September 05, 2019 by Steve Hoy

Delivery Options

Due to the increase in courier costs, we have found it necessary to raise the threshold for our Free Delivery.  From today free shipping is for orders over $249 -which pretty much covers all products bought by the box. Additionally, for those customers in regions not covered by our Free Delivery offer, we have recently added more shipping options that are at budget rates.  These rates are available now and you can be select the best rate at check-out.

August 09, 2019 by Addition Collaborator

Do You Need Any More Proof?

Check out this group submitted by Phil Wright and shot by Darren Scott with a CZ SP01 Orange. 10 shots from 15M one hole! Phil and Darren are part of the Cobram Pistol Club team heading to the VAPA state championships and all of them are using Tigershark's (no wonder with accuracy like this!).  Thanks for sharing the image Phil.

August 07, 2019 by Steve Hoy

Why is my clean brass not clean?

So before that knockers have their say, ultra clean shiny cases don't help you shoot better but handling fired cases can be hazardous as lead and other contaminants are easily transferred to the skin when reloading. Also, I'm not going to go into talking in detail about the pro's and con's of wet vs. dry (vibratory) cleaning except to say I have been wet tumbling for at least 3 years now and am very happy with how it works over dry, particularly how it cleans the inside of cases.  Not to mention the health benefits that go along with avoiding airborne lead that can be present when dry tumbling. 

Moving along, my recipe for cleaning used Lyman Turbo Sonic and Lemishine with 4KG of cases and 2L of water tumbled for 90 minutes which gave me pretty good results.   But in recent times I had started to notice that the brass wasn't coming out quite so well as it used to with cases not so shiny and kind of pale looking. I thought I'd try something else and bought some MP103 burnishing compound from Aussie Sapphire substituting it for the Lemishine/Turbo Sonic.  Although the results improved they were still not 100%

With not much else to do over breakfast, I researched (Googled) why this might be happening and, of course, with the internet full of opinions about recipes and what to use and not to use blah, blah I saw someone say that cleaning the media occasionally is a good idea.  Really? - aren't the pins cleaned in the process?  Anyway, no harm giving it a go so I threw in a couple of liters of water and a dishwashing tablet and in a few minutes that water had gone black!
See photo below.

I then proceeded to rinse and ran it through a wash cycle again this time I threw in some car wash (it was at hand) and ran it through again.  The water was now looking much clearer and with a final good rinse, I ran 4KG of dirty cases through using MP103 burnishing compound.  I set the tumbler for my usual 90 minutes.  10 minutes later I checked on progress and to my surprise, the cases looked clean already.  Grabbing one out of the soupy mix (using a spoon) its appearance was stunning!  I can't believe the difference. 

A good rinse and separation of media and you can see how they turned out - pretty well like new.  

 

 

July 12, 2019 by Steve Hoy
The Way of the Dodo

The Way of the Dodo

Following up from our earlier post about APS450 I have completed testing and have put together a report on my findings.

AP70N has long been my favourite for reloading 9MM, it has always performed well for me while others insist AP50 is better and some even preferring AP100.  

With the demise of AP70 the good news is that ADI has released the alternative to AP50 called APS450 and I thought it worthwhile to test it against 70 to see if it could bridge the gap till APS650 becomes available. Other powders were tested as part of the process as well.  For the full report click here

May 31, 2019 by Steve Hoy
The New ADI 450

The New ADI 450

According to ADI there is an imminent announcement about the future of AP70/100. Any gun shop will tell you that they are out of stock and can't get more so it looks as though AP70/100 is going the way of the Dodo. ADI is saying that there will be a replacement for 70 and 100 "soon" (APS650 and APS950) and admit it is a slow process and while many of us have good stock of 70/100 there are many who do not.  So I thought it'd be worth trying one of the new powders closest to my usual go-to choice of AP70 to see how it stacks up. 
APS450 is the replacement for AP50 and as close to AP70 as possible right now.

In comparison to AP70 in 9MM, preliminary testing is indicating that a decreased powder charge of around 0.1 to 0.2 grains is a good starting point for working up a load for APS450. For example, 3.8 of AP70 with a TGRSRK 135GN HP will run at a PF of 131.2 whereas a charge of 3.6 of APS450 will give a PF of 129.8. There are no guarantees that the results for each bullet weight will correlate exactly to a decrease from AP70 of 0.1 or 0.2 and further testing is required. Initial results are as per the picture below.

A full report with additional data and accuracy observations will follow.
May 12, 2019 by Steve Hoy

Brodie McIntosh wins at NSW IPSC State Titles

The NSW IPSC Handgun Championships was held in Albury at the Hume Pistol Club on April 5 -7 this year. 

The match was an IPSC International sanctioned Level 3 match consisting of 12 stages over 2 days. Hume Pistol club always puts on a good challenging match as this year lived up to past State Titles.

Brodie was successful in securing Open Overall Champion, Gold Medal Grand Master, and Presidents Medal. Brodie now has a short break before he then starts preparations for the 2019 Australasians in The Philippines later this year. 

(Brodie uses Tigershark 123GN RN) 

April 11, 2019 by Addition Collaborator

Tigershark 123 Gn HP's

You just can't get better than 123 Gn.HP's (9MM/38 Super) in an Open gun (major PF).  Here are 2 groups of 5 shots at around 18 meters from a rest.  Thanks, Tristan M. for sharing.  

March 29, 2019 by Addition Collaborator

New Packaging

Our next shipment arriving next week will be packed in our new boxes.  These boxes will present better in retail shops and will start shipping next week.  The first stock in this packaging will be 123HP's and over time we will gradually change over from the original plastic bags.

February 25, 2019 by Steve Hoy